Protective anode coatings for high energy batteries

ABSTRACT

Materials for coating a metal anode in a high energy battery, anodes coated with the materials, and batteries incorporating the coated anodes are provided. Also provided are batteries that utilize the materials as electrolytes. The coatings, which are composed of binary, ternary, and higher order metal and/or metalloid oxides, nitrides, fluorides, chlorides, bromides, sulfides, and carbides limit the reactions between the electrolyte and the metal anode in a battery, thereby improving the performance of the battery, relative to a battery that employs a bare anode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser. No. 16/081,533 filed Aug. 31, 2018, the entire contents of which are hereby incorporated by reference; U.S. patent application Ser. No. 16/081,533 is a National Stage of International Application No. PCT/US2017/021365 that was filed Mar. 8, 2017, the entire contents of which are hereby incorporated by reference; International Application No. PCT/US2017/021365 claims priority to U.S. provisional patent application No. 62/306,866 that was filed Mar. 11, 2016, the entire contents of which are hereby incorporated by reference.

REFERENCE TO GOVERNMENT RIGHTS

This invention was made with government support under DE-AC02-06CH11357 (Subcontract 9F-31901 from Argonne National Laboratories to Northwestern University) awarded by the Department of Energy and DMR1309957 awarded by the National Science Foundation. The government has certain rights in the invention.

BACKGROUND

The energy density of batteries is a critical bottleneck limiting the performance of portable electronics and electric vehicles. Lithium batteries offer superlative energy density, and for two decades, incremental improvements in materials, chemistry, and cell engineering have increased energy density from 250 to 650 Wh/L. While there are many ongoing efforts to increase energy density, most approaches offer only incremental improvements. For example, substituting a new Li₂MnO₃*LiMO₂ cathode material for state-of-the-art LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ offers only 7% improvement in cathode energy density. (See, Croy, J. R.; Abouimrane, A.; Zhang, Z. Next-Generation Lithium-Ion Batteries: the Promise of Near-Term Advancements. MRS bulletin 2014, 39, 407-415.) Similarly, substituting a new silicon-carbon composite anode for a conventional graphite anode offers only 20% improvement in cell energy density. (See, Obrovac, M. N.; Chevrier, V. L. Alloy Negative Electrodes for Li-Ion Batteries. Chem. Rev. 2014, 114, 11444-11502.)

Metal anodes, which are comprised entirely or almost entirely of the mobile element in a battery, present a rare opportunity for major improvement in energy density. For example, in a lithium battery with a LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ cathode, energy density can be doubled by substituting a lithium metal anode in place of a conventional graphite anode. (See, McCloskey, B. D. The Attainable Gravimetric and Volumetric Energy Density of Li—S and Li—Ion Battery Cells with Solid Separator-Protected Li-Metal Anodes. J. Phys. Chem. Lett. 2015, 6 (22), 4581-4588.) This doubling in energy density is attainable because metal anodes can eliminate host materials, polymeric binders, electrolyte-filled pores, and even copper current collectors from the anode. (See, Hovington, P.; Lagacé, M.; Guerfi, A.; Bouchard, P.; Mauger, A.; Julien, C. M.; Armand, M.; Zaghib, K. New Lithium Metal Polymer Solid State Battery for an Ultrahigh Energy: Nano C—LiFePO₄ Versus Nano Li_(1.2)V₃O₈ . Nano Lett. 2015, 15, 2671-2678.) Metal anodes also offer the lowest possible anode redox potential and therefore the highest possible cell voltage. In batteries where Na or Mg is the mobile element, metal anodes eliminate the need for anode host materials, which often exhibit poor capacity, kinetics, and reversibility for these elements. (See, Seh, Z. W.; Sun, J.; Sun, Y.; Cui, Y. A Highly Reversible Room-Temperature Sodium Metal Anode. ACS Cent. Sci. 2015, 1 (8), 449-455; Saha, P.; Datta, M. K.; Velikokhatnyi, O. I.; Manivannan, A.; Alman, D.; Kumta, P. N. Rechargeable Magnesium Battery: Current Status and Key Challenges for the Future. Progress in Materials Science 2014, 66, 1-86.)

A major challenge for the implementation of metal anodes is reactivity between the metals and electrolytes. Metal anodes must be electropositive to provide a sufficient cell voltage, but this electropositivity causes the metals to drive electrochemical reduction of electrolytes. Both liquid and solid electrolytes are often reactive at the anode surface. For graphite anodes in conventional lithium-ion batteries, reactivity can be mitigated by a passivation layer that forms in situ from the reaction products. This passivation layer must be mechanically durable, electronically insulating to block electron transfer from the anode to the electrolyte, and chemically stable or metastable. For metal anodes, there is sparse evidence for passivation by in situ reactivity. Reactivity at the surface of metal anodes causes impedance growth that destroys cell performance, according to Luntz et al. (See, Luntz, A. C.; Voss, J.; Reuter, K. Interfacial Challenges in Solid-State Li Ion Batteries. J. Phys. Chem. Lett. 2015, 6, 4599-4604.) These authors argue that “the principal hurdle for developing successful solid-state batteries for EVs is in minimizing the interfacial impedances between the [solid electrolyte] and the electrodes and not in maximizing the conductivity in the [solid electrolytes].”

To limit reactivity between metal anodes and electrolytes, coating materials can be deposited on the metal surface prior to cell assembly. These coatings typically range between one nanometer and one micrometer in thickness. Similar to passivation layers, these coatings should be durable and electronically insulating to block transfer of electrons. Unlike passivation layers, these coatings can be deposited at elevated temperatures from a variety of precursors, allowing for greater control of coating characteristics. Anode coatings function as an additional electrolyte layer and can be used in conjunction with other liquid or solid electrolytes. Li metal anodes have been protected with a variety of coatings including Li₃N, Li₃PO₄, and Al₂O₃. (See, Ma, G.; Wen, Z.; Wu, M.; Shen, C.; Wang, Q.; Jin, J.; Wu, X. Lithium Anode Protection Guided Highly-Stable Lithium-Sulfur Battery. Chem. Commun. 2014, 50, 14209-14212; Kuwata, N.; Iwagami, N.; Tanji, Y.; Matsuda, Y. Characterization of Thin-Film Lithium Batteries with Stable Thin-Film Li3PO4 Solid Electrolytes Fabricated by ArF Excimer Laser Deposition. J. Electrochem. Soc. 2010, 157 (4), A521-A527; Kozen, A. C.; Lin, C.-F.; Pearse, A. J.; Schroeder, M. A.; Han, X.; Hu, L.; Lee, S.-B.; Rubloff, G. W.; Noked, M. Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition. ACS nano 2015, 9 (6), 5884-5892; Kazyak, E.; Wood, K. N.; Dasgupta, N. P. Improved Cycle Life and Stability of Lithium Metal Anodes Through Ultrathin Atomic Layer Deposition Surface Treatments. Chem. Mater. 2015, 27, 6457-6462.) Anode coatings, like electrolytes, can also react with the anode metal. Thus, durable batteries with metal anodes require selection of anode coatings that are stable in contact with the anode metal.

SUMMARY

One aspect of the invention provides coated lithium metal anodes for high energy batteries. Also provided are batteries incorporating the coated lithium metal anodes.

One embodiment of a coated lithium metal anode includes: a lithium metal anode; and a coating on at least a portion of the lithium metal anode, wherein the coating comprises a metal sulfide selected from SrS, CaS, YbS, and combinations thereof. One embodiment of a lithium battery incorporating the coated lithium metal anode includes: the coated lithium metal anode; a cathode in electrical communication with the coated lithium metal anode; and an electrolyte disposed between the coated lithium metal anode and the cathode. The electrolyte can be, for example, a sulfide solid electrolyte.

Another embodiment of a coated lithium metal anode includes: a lithium metal anode; and a coating on at least a portion of the lithium metal anode, wherein the coating comprises a metal oxide selected from rare earth metal oxides, ternary lithium oxides other than Li₃PO₄, quaternary lithium oxides, calcium oxide, or a combination thereof, and further wherein the metal oxide is stable; exhibits chemical equilibrium with the lithium metal anode; and is electrically insulating. One embodiment of a lithium battery incorporating these coated lithium metal anodes includes: the coated lithium metal anode; a cathode in electrical communication with the coated lithium metal anode; and an electrolyte disposed between the coated lithium metal anode and the cathode. The coating can be composed of, for example, Li₂HfO₃ and/or Li₇La₃Hf₂O₁₂. The electrolyte can include, for example, a lithium salt in an organic solvent, such as a carbonate, an ether, or an acetal, or can be a solid electrolyte, such as a solid polymer electrolyte, an oxide solid electrolyte, a phosphate solid electrolyte, or a nitride solid electrolyte. Although, other electrolytes could be used. In one variation of this embodiment, the coating is composed of Li₇La₃Hf₂O₁₂ and the electrolyte is a Li₇La₃Zr₂O₁₂ oxide solid electrolyte. In some such variations, the anode coating material is a garnet-structured gradient material having the composition Li₇La₃Zr₂O₁₂ at the solid electrolyte interface and the composition Li₇La₃Hf₂O₁₂ at the lithium metal anode surface. The metal oxide coating can also be composed of, for example, a rare earth metal oxide having the formula R₂O₃, where R is selected from Dy, Er, Gd, Ho, La, Lu, Nd, Pr, Sm, Tm, and Y; or a rare earth metal oxide having the formula LiRO₂, where R is selected from Dy, Er, Gd, Ho, Sc, and Tb. The electrolyte can include, for example, a lithium salt in an organic solvent, such as a carbonate, an ether, or an acetal, or can be a solid electrolyte, such as a solid polymer electrolyte, an oxide solid electrolyte, a phosphate solid electrolyte, or a nitride solid electrolyte. Although other electrolytes could be used.

Another embodiment of a coated lithium metal anode includes: a lithium metal anode; and a coating on at least a portion of the lithium metal anode, wherein the coating comprises a metal halide selected from metal fluorides other than LiF, metal chlorides, and metal bromides, and the metal of the metal halide comprises an alkali metal, an alkaline earth metal, or a rare earth metal, and further wherein metal halide is stable; exhibits chemical equilibrium with the lithium metal anode; and is electrically insulating. One embodiment of a lithium battery incorporating these coated lithium metal anodes includes: the coated lithium metal anode; a cathode in electrical communication with the coated lithium metal anode; and an electrolyte disposed between the coated lithium metal anode and the cathode. The coating can be composed of, for example, a metal halide selected from CaF₂, SrF₂, YbF₂, EuF₂, or a combination thereof; YbCl₂; YbBr₂, BaBr₂, SrBr₂, EuBr₂, or a combination thereof; and/or LiCl, NaCl, KCl, RbCl, CsCl, or a combination thereof. The electrolyte can include, for example, a lithium salt in an organic solvent, such as a carbonate, an ether, or an acetal, or can be a solid electrolyte, such as a solid polymer electrolyte, an oxide solid electrolyte, a phosphate solid electrolyte, or a nitride solid electrolyte. Although, other electrolytes could be used. In some variations of these batteries, the electrolyte is a sulfide solid electrolyte.

Another embodiment of a coated lithium metal anode includes: a lithium metal anode; and a coating on at least a portion of the lithium metal anode, wherein the coating comprises a ternary lithium nitride, wherein the ternary lithium nitride is stable; exhibits chemical equilibrium with the lithium metal anode; and is electrically insulating. One embodiment of a lithium battery incorporating these coated lithium metal anodes includes: the coated lithium metal anode; a cathode in electrical communication with the coated lithium metal anode; and an electrolyte disposed between the coated lithium metal anode and the cathode. The coating can be composed of, for example, a ternary lithium nitride having the formula Li_(x)MN₄, wherein x is 5, 6, or 7 and M is an element selected from Ta, Nb, W, V, Re, and Mo; a ternary lithium nitride having the formula Li_(x)MN₂, wherein x is 2 or 3 and further wherein, when x is 2, M is selected from Zr, C, and Si, and when x is 3, M is Sc or B; and/or a ternary lithium nitride selected from LiMgN, Li₅Br₂N, Li₁₀BrN₃, Li₄SrN₂, Li₈TeN₂, or a combination thereof. The electrolyte can include, for example, a lithium salt in an organic solvent, such as a carbonate, an ether, or an acetal, or can be a solid electrolyte, such as a solid polymer electrolyte, an oxide solid electrolyte, a phosphate solid electrolyte, or a nitride solid electrolyte. Although, other electrolytes could be used.

Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the invention will hereafter be described with reference to the accompanying drawings.

FIGS. 1A and 1B depict thermodynamic concepts used for screening compounds. The stable convex hull is shown with a black dashed line. FIG. 1A illustrates stability for a candidate compound with respect to the set of nearest-energy competing phases. The competing phases are determined by removing the candidate compound and calculating a hypothetical convex hull, which is represented by the red dashed line. FIG. 1B illustrates equilibrium of a compound with Li metal, which requires a tie line between the compound and Li metal.

FIG. 2A shows the phase diagram for the Li—Al—O ternary system calculated at 400 K using compounds from the OQMD. FIG. 2B shows the phase diagram for the Li—Si—O ternary system calculated at 400 K using compounds from the OQMD. FIG. 2C shows the phase diagram for the Li—P—O ternary system calculated at 400 K using compounds from the OQMD. FIG. 2D shows the phase diagram for the Li—P—S ternary system calculated at 400 K using compounds from the OQMD. In these systems, no ternary phases exhibit tie lines with lithium metal. When a ternary Li-M-X (X=O, S) phase is combined with an excess of lithium metal, these phase diagrams show that the phase will react to form Li₂X and a metallic Li-M phase. These metallic phases allow continued electron transport from the lithium anode to the electrolyte and therefore continued reactivity.

DETAILED DESCRIPTION

Materials for coating the metal anode in a high energy battery, anodes coated with the materials, and batteries incorporating the coated anodes are provided. Also provided are batteries that utilize the materials as electrolytes.

The coatings, which are composed of binary, ternary, and higher order metal and/or metalloid oxides, nitrides, fluorides, chlorides, bromides, sulfides, and carbides can reduce the reactions between the electrolyte and active material of a metal anode, such as a lithium anode, a sodium anode, or a magnesium anode, in a metal battery, thereby improving the performance of the battery, relative to a battery that employs a bare anode.

A basic embodiment of a battery includes: a cathode; an anode in electrical communication with the cathode; and an electrolyte disposed between the anode and the cathode. If the electrolyte is not a solid electrolyte, the battery will typically also include a separator disposed between the anode and the cathode. The batteries include lithium metal batteries, sodium metal batteries, and magnesium metal batteries.

The electrolytes are ionically conductive materials and may include solvents, ionic liquids, metal salts, ions such as metal ions or inorganic ions, polymers, ceramics, and other components. An electrolyte may be an organic or inorganic solid or a liquid, such as a solvent (e.g., a non-aqueous solvent) containing dissolved salts.

Example salts that may be included in electrolytes for lithium metal batteries include lithium salts, such as LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, Li(FSO₂)₂N, LiC₄F₉SO₃, LiAlO₂, LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂) (C_(y)F_(2y−1)SO₂), (where x and y are natural numbers), LiCl, LiI, LiNO₃, and mixtures thereof. Non-aqueous electrolytes can include organic solvents, such as, cyclic carbonates, linear carbonates, fluorinated carbonates, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4 methyldioxolane, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethyleneglycol, dimethylether, and mixtures thereof.

Examples of solid-state electrolytes for lithium metal batteries include sulfide solid electrolytes, such as Li₃PS₄, Li₁₀GeP₂S₁₂, Li₆PS₅Br, Li₇P₂S₈I, Li₃PS₄, Li₁₀SiP₂S₁₂, Li₁₀SnP₂S₁₂, Li₆PS₅Cl, Li_(3.25)Ge_(0.25)P_(0.75)S₄, and Li_(3.4)Si_(0.4)P_(0.6)S₄; oxide solid electrolytes, such as Li₇La₃Zr₂O₁₂, LiLaTi₂O₆, Li₃PO₄, LiTi₂P₃O₁₂, Li_(1.3)Al_(0.3)Ti_(1.7)(PO₄)₃, Li_(0.34)La_(0.51)TiO_(2.94), and Li_(6.55)La₃Zr₂Ga_(0.15)O₁₂; and nitride solid electrolytes, such as Li₇PN₄. Further examples of sulfide solid-state electrolytes for lithium metal batteries include mixtures of xLi₂S*(1−x)P₂S₅ where x ranges from about 0.7 to about 0.8. Solid polymer electrolytes (SPEs) can also be used.

Examples of electrolytes for sodium metal batteries include NaPF₆ (sodium hexafluorophosphate) in glymes (e.g., mono-, di-, and tetraglyme), sodium hexafluorophosphate in glymes, and chloroaluminate ionic liquid electrolytes. Magnesium(II) bis(trifluoromethane sulfonyl) amide in triglyme is an example of an electrolyte for a magnesium metal battery.

The separators are typically thin, porous or semi-permeable, insulating films with high ion permeabilities. The separators can be composed of polymers, such as olefin-based polymers (e.g., polyethylene, polypropylene, and/or polyvinylidene fluoride). If a solid-state electrolyte, such as a solid polymer electrolyte or solid ceramic electrolyte, is, the solid-state electrolyte may also act as the separator and, therefore, no additional separator is needed.

The cathodes are composed of an active cathode material that takes part in an electrochemical reaction during the operation of the battery. The active cathode materials for lithium metal batteries may be lithium composite oxides and include layered-type materials, such as LiCoO₂, LiNi_(0.8)Co_(0.15)Al_(0.05)O₂, or Li_(1+x)Ni_(1−y−z)Co_(y)Mn_(z)O₂; olivine-type materials, such as LiFePO₄; spinel-type materials, such as LiMn₂O₄; and similar materials. The spinel-type materials include those with a structure similar to natural spinal LiMn₂O₄, that include a small amount nickel cation in addition to the lithium cation and that, optionally, also include an anion other than manganate. By way of illustration, such materials include those having the formula LiNi_((0.5−x))Mn_(1.5)M_(x)O₄, where 0≤x≤0.2 and M is Mg, Zn, Co, Cu, Fe, Ti, Zr, Ru, or Cr. Examples of cathode materials for sodium metal batteries include Na₃V₂(PO₄)₃, NaMnO₂, NaFePO₄, and Na₂S/activated carbon nanofibers. Examples of cathode materials for magnesium metal batteries include Mo₃S₄, TiSe₂, MgFePO₄F, MgFeSiO₄, MgCo₂O₄, and V₂O₅.

The metal anodes are composed of an active metals (i.e., Li, Na, or Mg), which provides a mobile element and takes part in an electrochemical reaction during the operation of the battery. The metal anodes can be pure, or substantially pure, metal (i.e., pure or substantially pure Li, Na, or Mg) or alloys of the active metal with one or more additional metal elements. In the metal alloys, the alloyed element or elements can be used to control dendrite formation, mechanical properties, surface chemistry, voltage, or other materials properties. For example, lithium may be alloyed with aluminum, indium, or sodium to form a lithium metal anode composed of a lithium metal alloy. Alloyed metal anodes may include a majority or a minority of lithium. In some embodiments of the metal alloys, the active metal makes up a majority (i.e., >50%) of the alloy by weight, while in other embodiments the other metal elements make up a majority of the alloy by weight.

The active anode material is at least partially coated with a continuous or discontinuous anode coating of a metal compound and/or metalloid compound. The coatings allow diffusion of the mobile metal ions (e.g., Li, Na, or Mg ions) between the anode and electrolyte, while blocking diffusion of electrons and other species that cause electrochemical or chemical reactions between the anode and the electrolyte. The coatings may also limit spatial irregularities at the anode-electrolyte interface that can lead to metal dendrites and internal short circuits. The coatings thereby create a more stable anode-electrolyte interface to enhance the durability, cycle life, calendar life, power, and/or safety of the cell. The coating compounds desirably have a high bandgap because compounds with higher bandgaps are more likely to maintain electronic insulation in the harsh chemical environment of a battery. By way of illustration, some of the coating compounds have bandgaps of at least 1 eV. This includes compounds having a bandgap of at least 2 eV, at least 3 eV, at least 4 eV, at least 5 eV, at least 6 eV, at least 7 eV, at least 8 eV, and at least 9 eV.

The coating compounds may be selected from compounds that are stable; exhibit chemical equilibrium with the metal anode; are electronic insulators; and, desirably do not contain radioactive elements. The meaning of the terms “stable”, “exhibits chemical equilibrium with the metal anode” and “electronic insulator”, as used herein, are provided in Example 1, which described in detail the methods and calculations that can be used to evaluate these properties. Briefly, a coating compound is stable if it has a formation energy lower than any other phase or combination of phases at the composition of the candidate compound, as identified using the convex hull methods. A coating compound exhibits chemical equilibrium with a metal anode if it is not consumed to any significant extent by a chemical reaction with that anode. This is determined by calculating the convex hull for the set of elements defined by the compound and the metal anode and determining if a tie line connects the coating compound with the metal of the anode. The existence of a tie lie indicates that the compound exhibits stable equilibrium with the metal anode. Finally, a coating compound is considered to be an electronic insulator if it has a DFT Kohn-Sham bandgap, as tabulated in the Open Quantum Materials Database of at least 1.0 eV.

These properties of the coating materials also render the coating materials suitable for use as electrolytes in the batteries. Therefore, the coatings are able to act as an additional electrolyte layer in the battery. Alternatively, metal batteries can employ the anode coating materials described herein as electrolytes, rather than, or in addition to, anode coatings.

The compounds include binary, ternary and quaternary metal and/or metalloid oxides, nitrides, halides (e.g., fluorides, chlorides, and bromides), sulfides, and carbides, including compounds in which the metal is an alkali metal, an alkaline earth metal, a transition metal, a post-transition metal, and/of a rare earth metal. Suitable metals include the metal from which the active anode material is composed. The coating compounds may be used as pure single phases, combined as atomically mixed phases, or combined as composite mixed phases.

The oxides are compounds of one or more metal and/or metalloid elements and oxygen. In some embodiments of the coatings, the oxide compounds have the formula MO, where M is a metal, such as, for example, an alkaline earth metal, or a rare earth metal. In some embodiments of the coatings, the oxide compounds have the formula M₂O₃, wherein M is a metal, such as a rare earth metal. In some embodiment of the coatings for lithium anodes, the oxide compounds have the formula LiRO₂, where R is a rare earth metal. Similarly, in some embodiments of the coatings for sodium anodes, the oxide compounds have the formula NaRO₂, where R is a rare earth metal.

The nitrides are compounds of one or more metal and/or metalloid elements and nitrogen. In some embodiments of the coatings for lithium anodes, the nitride compounds have the formula Li_(x)MN₄, where x is 5, 6, or 7 and M is a metal, such as Ta, Nb, W, V, Re, or Mo.

The sulfides are compounds of one or more metal and/or metalloid elements and sulfur. In some embodiments of the coatings for sodium anodes, the sulfide compounds have the formula NaRS₂, where R is a rare earth metal.

The chlorides are compounds of one or more metal and/or metalloid elements and chlorine. In some embodiments of the coatings for magnesium anodes, the chloride compounds have the formula RCl₃, where R is a rare earth metal.

Similarly, the fluorides are compounds of one or more metal and/or metalloid elements and fluorine; the bromides are compounds of one or more metal and/or metalloid elements and bromine; and the carbides are compounds of one or more metal and/or metalloid elements and carbon.

The performance and lifetime of a battery can be still further enhanced if the coating is chemically stable and exhibits chemical equilibrium with respect to the electrolyte, as well as with the active anode metal. Therefore, in some embodiments of the coated metal anodes, the electrolyte is selected such that the coating compounds are stable and exhibit chemical equilibrium with respect to the electrolyte. This is demonstrated in the Example 2, for certain solid-state electrolytes for lithium batteries.

The compounds can be synthesized and formed as coatings using known methods for forming coatings on anodes and other substrates. The coatings can be formed directly on the anode active material or formed on the electrolyte material and subsequently contacted with the metal anode. For the purposes of this disclosure the latter situation is considered a coating on the metal anode by virtue of the contact of the coating with the surface of a active anode material.

Some embodiments of the coating materials, such as metal oxides and metalloid oxides and nitrides, including binary and ternary oxides and nitrides, can be applied to the anode active material via atomic layer deposition (ALD) using known precursors. By way of illustration, compounds of the formula M₂O₃, including compounds where M is a rare earth metal element, can be formed via ALD. Other methods for forming coatings include the solution phase reaction of a cation precursor with an anion precursor in the presence of the anode active material. Because conventional metal anodes take the form of a thin foil, vapor deposition (e.g., chemical vapor deposition, physical vapor deposition, and/or pulsed laser deposition) is well suited for the deposition of the anode coating materials on the anode substrates. However, powder deposition can also be used. Some embodiments of the coating materials can be applied to the anode active material using both external precursors and internal precursors that are alloyed with the metal anode materials and can segregate to the surface of the anode to partially form the coating.

It the metal anode is a particulate material, for example a metal or metal alloy particles embedded in a composite structure, a coated anode can be made by forming a reaction mixture that includes the anode active material particles, a cation precursor, and an anion precursor in a solvent and initiating a precipitation reaction between the cation precursor and the anion precursor to form the anode coating material on the anode active material. If the metal andoe is in the form of a thin foil, a mixture of the cation precursor and the anion precursor can be applied to the surface of the foil and the precipitation reaction can be initiated there. Alternatively, the anode coating compounds can be formed in the absence of the anode active material and subsequently combined with the anode active material to form a composite in which the anode coating materials are in contact with and at least partially surround particles of the anode active material. The coating methods can, optionally, include grinding a mixture of anode coating material and anode active material and calcining the product.

The coatings may be sufficiently thick that that the bulk of the coating away from the interface between the anode active material and the anode coating material preserves the nominal coating composition. By way of illustration, some embodiments of the anode coatings have a thickness in the range from 0.1 to 1000 nm, including thicknesses in the range from 0.2 to 500 nm, and from 1 to 200 nm. The amount of anode coating material based on weight may be, for example, in the range from 0.01 to 40% based on the mass of the anode active material. This includes anode coatings in which the amount of anode coating material is in the range from 0.1 to 30%, based on the mass of the anode active material, and further includes anode coatings in which the amount of anode coating material is in the range from 1 to 15%, based on the mass of the anode active material.

The Summary section of this disclosure provides illustrative examples of some embodiments of coated lithium metal anodes and lithium batteries incorporating the coated lithium metal anodes. The immediately following description provides illustrative examples of some embodiments of coated sodium metal anodes and coated magnesium metal anodes, as well as sodium and magnesium batteries incorporating the coated metal anodes.

One embodiment of a coated sodium metal anode includes: a sodium metal anode; and a coating on at least a portion of the sodium metal anode, wherein the coating comprises a rare earth metal oxide, and further wherein the rare earth metal oxide is stable; exhibits chemical equilibrium with the sodium metal anode; and is electrically insulating. The coating can be composed of, for example, a rare earth metal oxide having the formula R₂O₃ or the formula NaRO₂, where R is a rare earth metal element. Another embodiment of a coated sodium metal anode includes: a sodium metal anode; and a coating on at least a portion of the sodium metal anode, wherein the coating comprises a binary metal oxide selected from, for example, CaO, SrO, YbO, BaO, and combinations thereof, and further wherein the binary metal oxide is stable; exhibits chemical equilibrium with the sodium metal anode; and is electrically insulating. Yet another embodiment of a coated sodium metal anode includes: a sodium metal anode; and a coating on at least a portion of the sodium metal anode, wherein the coating comprises a ternary sodium oxide selected from, for example, of Na₂ZrO₃, Na₄WO₅, Na₄SiO₄, Na₃BO₃, Na₇Al₃O₈, Na₅TaO₅, Na₅NbO₄, Na₅AlO₄, Na₃ClO, Na₂Hf₂O₅, Na₄Br₂O, and combinations thereof, and further wherein the ternary sodium oxide is stable; exhibits chemical equilibrium with the sodium metal anode; and is electrically insulating. One embodiment of a sodium battery incorporating these coated sodium metal anodes includes: the coated sodium metal anode; a cathode in electrical communication with the coated sodium metal anode; and an electrolyte disposed between the coated sodium metal anode and the cathode.

Another embodiment of a coated sodium metal anode includes: a sodium metal anode; and a coating on at least a portion of the sodium metal anode, wherein the coating comprises a binary metal sulfide selected from, for example, Na₂S, SrS, CaS, YbS, BaS, EuS, and combinations thereof, and further wherein the binary metal sulfide is stable; exhibits chemical equilibrium with the sodium metal anode; and is electrically insulating. Another embodiment of a coated sodium metal anode includes: a sodium metal anode; and a coating on at least a portion of the sodium metal anode, wherein the coating comprises a ternary sodium sulfide selected from, for example, NaLiS, NaLuS₂, NaErS₂, NaHoS₂, NaYS₂, or NaTmS₂, and combinations thereof, and further wherein the ternary sodium sulfide is stable; exhibits chemical equilibrium with the sodium metal anode; and is electrically insulating. One embodiment of a sodium battery incorporating the coated sodium metal anode includes: the coated sodium metal anode; a cathode in electrical communication with the coated sodium metal anode; and an electrolyte disposed between the coated sodium metal anode and the cathode. The electrolyte can be, for example, a sulfide solid electrolyte.

Another embodiment of a coated sodium metal anode includes: a sodium metal anode; and a coating on at least a portion of the sodium metal anode, wherein the coating comprises a metal fluoride, such as LiF, NaF, EuF₂, SrF₂, CaF₂, YbF₂, BaF₂, or a combination thereof, and further wherein the metal fluoride is stable; exhibits chemical equilibrium with the sodium metal anode; and is electrically insulating. One embodiment of a sodium battery incorporating these coated sodium metal anodes includes: the coated sodium metal anode; a cathode in electrical communication with the coated sodium metal anode; and an electrolyte disposed between the coated sodium metal anode and the cathode.

Another embodiment of a coated sodium metal anode includes: a sodium metal anode; and a coating on at least a portion of the sodium metal anode, wherein the coating comprises a ternary sodium nitride, such as Na₂CN₂, Na₃WN₃, Na₃BN₂, Na₃MoN₃, NaTaN₂, or a combination thereof, and further wherein the ternary sodium nitride is stable; exhibits chemical equilibrium with the sodium metal anode; and is electrically insulating. One embodiment of a sodium battery incorporating these coated sodium metal anodes includes: the coated sodium metal anode; a cathode in electrical communication with the coated sodium metal anode; and an electrolyte disposed between the coated sodium metal anode and the cathode.

One embodiment of a coated magnesium metal anode includes: a magnesium metal anode; and a coating on at least a portion of the magnesium metal anode, wherein the coating comprises a metal sulfide selected from, for example, Lu₂MgS₄, MgS, SrS, CaS, YbS, and combinations thereof, and further wherein the metal sulfide is stable; exhibits chemical equilibrium with the magnesium metal anode; and is electrically insulating. One embodiment of a magnesium battery incorporating the coated magnesium metal anode includes: the coated magnesium metal anode; a cathode in electrical communication with the coated magnesium metal anode; and an electrolyte disposed between the coated magnesium metal anode and the cathode. The electrolyte can be, for example, a sulfide solid electrolyte.

Another embodiment of a coated magnesium metal anode includes: a magnesium metal anode; and a coating on at least a portion of the magnesium metal anode, wherein the coating comprises a ternary magnesium fluoride or a ternary magnesium chloride, such as KMgF₃, NaMgF₃, RbMgF₃, Mg₃NF₃, CsMgCl₃, Cs₂MgCl₃, K₂MgCl₄, or a combination thereof, and further wherein the ternary magnesium fluoride or ternary magnesium chloride is stable; exhibits chemical equilibrium with the magnesium metal anode; and is electrically insulating. One embodiment of a magnesium battery incorporating these coated magnesium metal anodes includes: the coated magnesium metal anode; a cathode in electrical communication with the coated magnesium metal anode; and an electrolyte disposed between the coated magnesium metal anode and the cathode.

Another embodiment of a coated magnesium metal anode includes: a magnesium metal anode; and a coating on at least a portion of the magnesium metal anode, wherein the coating comprises a magnesium nitride, such as Mg₃N₂, MgSiN₂, or a combination thereof, and further wherein the magnesium nitride is stable; exhibits chemical equilibrium with the magnesium metal anode; and is electrically insulating. One embodiment of a magnesium battery incorporating these coated magnesium metal anodes includes: the coated magnesium metal anode; a cathode in electrical communication with the coated magnesium metal anode; and an electrolyte disposed between the coated magnesium metal anode and the cathode.

Another embodiment of a coated magnesium metal anode includes: a magnesium metal anode; and a coating on at least a portion of the magnesium metal anode, wherein the coating comprises a ternary magnesium carbide, such as MgAl₂C₂, MgB₂C₂, or a combination thereof, and further wherein the ternary magnesium carbide is stable; exhibits chemical equilibrium with the magnesium metal anode; and is electrically insulating. One embodiment of a magnesium battery incorporating these coated magnesium metal anodes includes: the coated magnesium metal anode; a cathode in electrical communication with the coated magnesium metal anode; and an electrolyte disposed between the coated magnesium metal anode and the cathode.

EXAMPLES Example 1: Coatings for Lithium, Sodium, and Magnesium Metal Anodes

In this example, the Open Quantum Materials Database (OQMD) was screened to identify coatings that exhibit chemical equilibrium with the anode metals and are electronic insulators. The coatings were ranked according to their electronic bandgap. Ninety-two coatings for Li anodes were identified, 118 for Na anodes, and 97 for Mg anodes. Only two compounds that are commonly studied as Li solid electrolytes passed these screens: Li₃N and Li₇La₃Hf₂O₁₂. Many of the coatings that were identified are new to the battery literature. Notably, the OQMD is compiled from compounds that had previously been synthesized, therefore this database can be used as a resource for references describing methods of making compounds of the type described herein.

The Open Quantum Materials Database was searched to identify electronically insulating materials that exhibit stable equilibrium with metal anodes made of Li, Na, and Mg. It was found that many materials currently used in Li batteries as electrode coatings or solid electrolytes are reactive with Li metal to form unanticipated reaction products, including electronically conductive phases that facilitate continued transfer of electrons from the anode to the electrolyte. Ninety-two coatings were identified for Li anodes, 118 for Na anodes, and 97 for Mg anodes. These coatings included binary, ternary, and quaternary compounds. For Li anodes, Li-containing ternary coatings were identified, including seven oxides and 21 nitrides, but no fluorides or sulfides. For Na anodes, Na-containing ternaries were identified, including 26 oxides, nine nitrides, and six sulfides, but no fluorides. For Mg anodes, Mg-containing ternaries were identified, including five fluorides, four nitrides, and one sulfide, but no oxides. A variety of chloride, bromide, and carbide coatings for the anodes were also identified. Only two compounds that are commonly studied as Li solid electrolytes passed these screens: Li₃N and Li₇La₃Hf₂O₁₂. Many of the coatings that were identified are new to the battery literature.

Methodology Calculation of Formation Energies

The Open Quantum Materials Database (OQMD) was screened to identify coating materials for Li, Na, and Mg metal anodes. The OQMD is a publicly-available database of more than 440,000 compounds containing various materials properties, calculated using density functional theory (DFT). (See, Saal, J. E.; Kirklin, S.; Aykol, M.; Meredig, B.; Wolverton, C. Materials Design and Discovery with High-Throughput Density Functional Theory: the Open Quantum Materials Database (OQMD). JOM 2013, 65 (11), 1501-1509; Kirklin, S.; Saal, J. E.; Meredig, B.; Thompson, A.; Doak, J. W.; Aykol, M.; Rühl, S.; Wolverton, C. The Open Quantum Materials Database (OQMD): Assessing the Accuracy of DFT Formation Energies. Nature Publishing Group 2015, 1 (15010), 1-15.) (The details of the various parameters used to perform the DFT calculations are discussed elsewhere. (See, Kirklin, S.; Saal, J. E.; Meredig, B.; Thompson, A.; Doak, J. W.; Aykol, M.; Rühl, S.; Wolverton, C. The Open Quantum Materials Database (OQMD): Assessing the Accuracy of DFT Formation Energies. Nature Publishing Group 2015, 1 (15010), 1-15; Grindy, S.; Meredig, B.; Kirklin, S.; Saal, J. E.; Wolverton, C. Approaching Chemical Accuracy with Density Functional Calculations: Diatomic Energy Corrections. Phys. Rev. B 2013, 87 (7), 075150; Perdew, J.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865-3868; Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50 (24), 17953; Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B 1999, 59 (3), 1758; Kresse, G.; Hafner, J. Ab Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47 (1), 558-561; Kresse, G.; Hafner, J. Ab Initio Molecular-Dynamics Simulation of the Liquid-Metal-Amorphous-Semiconductor Transition in Germanium. Phys. Rev. B 1994, 49 (20), 14251; Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Computational Materials Science 1996, 6, 15-50; Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54 (16), 11169; Anisimov, V. I.; Zaanen, J.; Andersen, O. K. Band Theory and Mott Insulators: Hubbard U Instead of Stoner I. Phys. Rev. B 1991, 44 (3), 943; Anisimov, V.; Solovyev, I.; Korotin, M.; Czyżyk, M.; Sawatzky, G. Density-Functional Theory and NiO Photoemission Spectra. Phys. Rev. B 1993, 48 (23), 16929; Liechtenstein, A.; Anisimov, V.; Zaanen, J. Density-Functional Theory and Strong Interactions: Orbital Ordering in Mott-Hubbard Insulators. Phys. Rev. B 1995, 52 (8), 5467-5470; Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C. J.; Sutton, A. Electron-Energy-Loss Spectra and the Structural Stability of Nickel Oxide: an LSDA+ U Study. Phys. Rev. B 1998, 57 (3), 1505-1509.) The formation energy of a compound A_(a)B_(b) C_(c) . . . Z_(z), ΔH_(f) was calculated using

${\Delta \; {H_{f}\left( {A_{a}B_{b}C_{c}\mspace{14mu} \ldots \mspace{14mu} Z_{z}} \right)}} = {{E\left( {A_{a}B_{b}C_{c}\mspace{14mu} \ldots \mspace{14mu} Z_{z}} \right)} - {\sum\limits_{i = A}^{Z}{\alpha_{i}\mu_{i}}}}$

where E (A_(a)B_(b)C_(c) . . . Z_(z)) is the DFT energy of the compound from the OQMD, α_(u) is the atom fraction of element i in the compound, and μ_(i) is the chemical potential of element i, from the OQMD. The reference chemical potential of elements whose state at room temperature is different from that at 0 K (gaseous elements, and elements that undergo a phase transformation below room temperature) were fit to experimental formation enthalpies at standard temperature and pressure in the OQMD. (See, Kirklin, S.; Saal, J. E.; Meredig, B.; Thompson, A.; Doak, J. W.; Aykol, M.; Rühl, S.; Wolverton, C. The Open Quantum Materials Database (OQMD): Assessing the Accuracy of DFT Formation Energies. Nature Publishing Group 2015, 1 (15010), 1-15.) Further, the free energies of F, O, Cl, N, and Br were adjusted to their reference states at 1 atm and 400 K, by adding enthalpy and entropy corrections from the JANAF Thermochemical Tables. (See, Chase, M. W.; Davies, C. A.; Downey, J. F.; Frurip, D. J.; McDonald, R. A.; Syverud, A. N. JANAF Thermochemical Tables; 1985.) The temperature of 400 K was selected to reflect conditions of vapor deposition on lithium metal and to reflect the maximum operating temperature of solid state batteries.

Screening Criteria

The screening strategy that was used employed four main criteria to identify potential anode coatings materials: (a) stability, (b) equilibrium with the anode metal, (c) electronic insulation, and (d) lithium content. Additionally, all compounds with radioactive elements were discarded: Pm, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, and Bk. The screening criteria are described in detail below.

Stability: The search for anode coatings was limited to compounds that are stable, because stable compounds are most amenable to synthesis. By definition, a candidate compound is stable if it has a formation energy lower than any other phase or combination of phases at the composition of the candidate compound. Stable compounds were identified using the convex hull method, considering all compounds in the OQMD. Stable compounds were further quantified by calculating a numerical value for stability. The stability of a candidate compound was calculated by taking the numerical difference between the formation energy of the candidate compound minus the formation energy of the lowest-energy set of competing phases. The competing phases were determined by considering all compounds in the OQMD, but removing the candidate compound and other phases at the candidate compound's composition, and then calculating the lowest-energy set of phases at the candidate compound's composition. Stability was negative for stable compounds, as illustrated in FIG. 1A.

Equilibrium: In addition to calculating the stability of a compound, it was also determined whether a compound exhibits chemical equilibrium with the anode metals: Li, Na, and Mg. Stability of a compound and equilibrium of the compound with a metal anode are two distinct concepts that are sometimes confused. A given solid electrolyte material may be stable when synthesized in isolation; however, when such a solid electrolyte material is combined with a metal anode, it may still be consumed by a chemical reaction. Such a material is stable, but it does not exhibit equilibrium with the anode metal. To compute whether a compound exhibits equilibrium with an anode metal, the convex hull method was again used. For each candidate compound, the convex hull was calculated for the set of elements defined by the compound plus the anode metal. Within this convex hull, a tie line connecting the candidate compound with the anode metal was searched for. The presence of such a tie line was taken as an indication that the candidate compound does exhibit stable equilibrium with the anode metal. The absence of such a tie line was taken as an indication that the candidate compound does not exhibit stable equilibrium with the anode metal, but rather reacts with the anode metal. Equilibrium with an anode metal is illustrated in FIG. 1B.

Electronic Insulation: To identify coatings that are electronically insulating, compounds that contain F, O, Cl, N, Br, S, or C were targeted in the search. The DFT Kohn-Sham bandgap was considered, as tabulated in the OQMD. (See, Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Physical Review 1965, 140 (4A), A1133-A1138.) Compounds that exhibit a bandgap above 1.0 eV were screened for. This somewhat lenient bandgap value was selected because the Kohn-Sham bandgap with the PBE functional systemically underestimates the experimental bandgap with a mean absolute error of 0.84 eV. (See, Chan, M.; Ceder, G. Efficient Band Gap Prediction for Solids. Phys. Rev. Lett. 2010, 105, 196403.) Compounds were ranked according to bandgap because compounds with higher bandgaps are more likely to maintain electronic insulation in the harsh chemical environment of a battery, while compounds with smaller bandgaps may become doped and electronically conductive.

Lithium Content: Compounds that contain the anode metal were screened for because all notable solid electrolytes in the lithium battery literature contain lithium sublattices, which enable lithium diffusivity. This requirement for Li content was relaxed for binary compounds to expand our results beyond the binaries, such as LiF, etc.

During the screening, many compounds were rejected that lacked equilibrium with lithium metal. These rejected compounds included many that appear in the lithium battery literature as notable solid electrolytes or electrode coatings. A variety of these compounds were examined and their reactions with lithium metal were computed. Reaction products were determined by combining each compound with an excess of lithium metal and computing the equilibrium set of phases. The excess of lithium was specified to reflect a lithium metal anode in equilibrium with a relatively thin coating. Lithium metal anodes are typically micrometers in thickness; whereas, anode coatings are typically nanometers in thickness. Li₁₀GeP₂S₁₂ and LiLaTi₂O₆ were not available in the OQMD, so for these reactions, formation energies were used from the Materials Project. (See, Jain, A.; Ong, S. P.; Hautier, G.; Chen, W.; Richards, W. D.; Dacek, S.; Cholia, S.; Gunter, D.; Skinner, D.; Ceder, G.; et al. Commentary: the Materials Project: a Materials Genome Approach to Accelerating Materials Innovation. APL Mater. 2013, 1, 011002; Ong, S. P.; Wang, L.; Kang, B.; Ceder, G. Li—Fe—P—O2 Phase Diagram From First Principles Calculations. Chem. Mater. 2008, 20, 1798-1807; Jain, A.; Hautier, G.; Ong, S. P.; Moore, C. J.; Fischer, C. C.; Persson, K. A.; Ceder, G. Formation Enthalpies by Mixing GGA and GGA+ U Calculations. Phys. Rev. B 2011, 84, 045115.)

Results and Discussion

It was found that many solid electrolyte and electrode coating materials in the lithium battery literature, including oxides and sulfides, are reactive with lithium metal. Table 1 lists these reactions and corresponding reaction energies, which range from −18 to −714 meV/atom. The list includes two sulfide compounds, which exhibit the two highest reaction energies. Compounds that are reactive with lithium metal include notable solid electrolytes such as Li₇La₃Zr₂O₁₂ (LLZO), LiLaTi₂O₆ (LLTO), and Li₁₀GeP₂S₁₂ (LGPS) as well as notable electrode coatings such as Al₂O₃, Li₃PO₄, and LiAlO₂. Each compound yields two or three reaction products including Li₂O for oxides and Li₂S for sulfides. Besides Li₂O or Li₂S, the remaining reaction products typically include at least one phase that is electronically conductive. These electronically conductive phases, when formed on the anode surface, facilitate electron transfer from the anode to the electrolyte. This electron transfer allows continued reactivity and prevents passivation of the anode/electrolyte interface. Only one compound in Table 1, LLZO, yields reaction products that are all electronically insulating and therefore capable of passivating the surface of lithium metal. This is consistent with experiments reported by Luntz et al. A list of solid electrolytes was considered, including LLZO, LGPS, lithium phosphorous oxynitride (LiPON), and Li₃ClO and it was found that only LLZO “appears to be chemically stable to reduction by lithium metal.” (See, Luntz, A. C.; Voss, J.; Reuter, K. Interfacial Challenges in Solid-State Li Ion Batteries. J. Phys. Chem. Lett. 2015, 6, 4599-4604.) The results support and clarify this experimental finding, showing that LLZO is resistant to reduction by lithium metal due to passivation. However, anode coatings at the interface between lithium metal and LLZO can improve the properties of the interface and improve battery performance.

TABLE 1 Compounds that are commonly tested as electrode coatings and solid electrolyes in lithium batteries often react with lithium metal anodes. The corresponding reactions and reaction energies (meV/atom) are listed. Most reaction products include electronically conductive phases, which can hinder passivation of the lithium metal surface and facilitate further reactivity. The existence of such conductive reaction products is indicated in the last column. Con- Compound Reaction ΔE^(rxn) ductive Li₃PS₄ Li₃PS₄ + 8*Li → 4*Li₂S + Li₃P −714 Yes Li₁₀GeP₂S₁₂ Li₁₀GeP₂S₁₂ + 23.75*Li → 12*Li₂S + −642 Yes 2*Li₃P + 0.25*Li₁₅Ge₄ ZnO ZnO + 3*Li → Li₂O + LiZn −613 Yes Li₃PO₄ Li₃PO₄ + 8*Li → 4*Li₂O + Li₃P −338 Yes SiO₂ SiO₂ + 41/5*Li → 2*Li₂O + ⅕*Li₂₁Si₅ −332 Yes LiLaTi₂O₆ LiLaTi₂O₆ + 14/3*Li → 17/6*Li₂O + −164 Yes LaTiO₃ + ⅙*Ti₆O Al₂O₃ Al₂O₃ + 10.5*Li → 3*Li₂O + −152 Yes 0.5*Li₉Al₄ Li₇La₃Zr₂O₁₂ Li₇La₃Zr₂O₁₂ + 2*Li → 4.5*Li₂O + −138 No (LLZO) 0.5*La₂O₃ + 2*LaZrO₃ Li₄SiO₄ Li₄SiO₄ + 41/5*Li → 4*Li₂O + −105 Yes ⅕*Li₂₁Si₅ LiAlO₂ LiAlO₂ + 21/4*Li → 2*Li₂O + −62 Yes ¼*Li₉Al₄ MgO MgO + 7*Li → Li₂O + Li₅Mg −18 Yes

The tendency of oxide and sulfide compounds to react with lithium metal to form Li₂O or Li₂S highlights the difficulty in finding compounds that exhibit equilibrium with lithium metal. This tendency is illustrated by the Li—Al—O, Li—Si—O, Li—P—O, and Li—P—S phase diagrams shown in FIGS. 2A, 2B, 2C, and 2D, respectively. These phase diagrams contain a variety of ternary phases, which might otherwise have good properties for coatings, except that none of these phases share a tie line with Li metal. In these phase diagrams, Li metal shares tie lines only with Li₂O or Li₂S plus metallic phases, which prevent passivation.

Ninety-two promising coatings for Li metal anodes were identified, as well as 118 promising coatings for Na metal anodes, and 97 promising coatings for Mg anodes. These coatings include binary, ternary, and quaternary compounds. The tally of coatings is resolved for each anode/anion pair in Table 2. At least one binary coating passed the screens for each anode/anion pair. Ternary compounds passed the screens for all pairs except Li/F, Na/F, Li/S, and Mg/O. Quaternary compounds passed the screens only for Li/O, Li/N, Li/C, Na/O, and Na/N. Some compounds that passed the screens contained multiple anions from the list, including six coatings identified for Li metal, six coatings identified for Na metal, and one coating identified for Mg metal.

Nine pentary compounds passed the screens across the Li/N, Li/Br, Li/C, and Na/O pairs, but all of these pentaries had low concentrations of Li and Na, for example, LiEu₂CBr₃N₂ or KNaLaTaO₅. Therefore, an additional screen was imposed to exclude compounds with five or more elements.

TABLE 2 Tally of compounds that were identified as promising coatings for Li, Na, and Mg metal anodes. The tally is resolved according to the anode metal, the anion, and the number of elements in the compound. Anions Anodes F O Cl N Br S C Li Binaries 5 16 9 4 9 6 1 Ternaries 0 7 1 21 2 0 2 Quaternaries 0 4 0 10 0 0 1 Na Binaries 7 24 5 10 5 7 3 Ternaries 0 26 1 9 1 6 1 Quaternaries 0 13 0 6 0 0 0 Mg Binaries 11 14 21 4 18 11 2 Ternaries 5 0 4 4 1 1 2 Quaternaries 0 0 0 0 0 0 0

For Li metal anodes, Tables 3-9 list the binary and ternary compounds that passed the screens containing F, O, Cl, N, Br, S, and C anions, respectively. Table 10 lists all quaternary compounds for lithium metal anodes, which included O, N, and C anions. Across all 92 compounds that passed the screens for Li anodes, only two compounds are commonly studied as solid electrolytes: Li₃N and Li₇La₃Hf₂O₁₂. Li₃N is known to exhibit high Li diffusivity. However, the low bandgap for Li₃N (1.2 eV by DFT, 2.2 eV by experiment) may be susceptible to electronic doping on a Li metal anode. Furthermore, Li₃N is not chemically stable with many electrolytes. Li₇La₃Hf₂O₁₂ is a lesser-known member of the garnet family, which also contains compounds such as Li₇La₃Zr₂O₁₂, Li₅La₃Nb₂O₁₂, and Li₅La₃Ta₂O12, which have received more attention in the solid electrolyte literature. The finding of equilibrium with Li metal for the garnet Li₇La₃Hf₂O₁₂ is somewhat surprising, given that the better-studied Li₇La₃Zr₂O₁₂ garnet does not exhibit equilibrium with Li metal. The competing phases for Li₇La₃Hf₂O₁₂ are Li₂O, La₂O₃, and Li₂HfO₃. All three of these competing phases also exhibit equilibrium with Li metal, providing additional assurance for Li₇La₃Hf₂O₁₂ as a robust coating on Li metal. Also proposed is a Li₇La₃M₂O₁₂ (M=Hf, Zr) garnet solid electrolyte that is rich in Hf near the anode for chemical equilibrium but rich in Zr away from the anode for greater Li conductivity.

According to the findings, Li₇La₃Hf₂O₁₂ qualifies as a coating and therefore may be employed as a solid electrolyte in direct contact with Li metal without the need for any other intervening anode coating. However, for other electrolytes that lack equilibrium with Li metal, such as those listed in Table 1 as well as various liquid electrolytes, an intervening anode coating was needed to prevent electrochemical reduction of the electrolyte. The compounds identified in Tables 3-10 can be employed as anode coatings to stabilize such anode/electrolyte interfaces.

Throughout the 92 compounds identified as coatings for Li metal anodes, a few classes of compounds can be distinguished. Within the 16 binary oxides, 11 are members of R₂O₃ where R is a rare earth elements including Y, Lu, Dy, Tm, Ho, Er, Gd, Nd, Sm, Pr, and La. CaO is unique among the oxide coatings for lithium metal in that it contains only low-cost and non-toxic elements. Within the seven ternary oxides, six are members of LiRO₂, where R is a rare earth element including Gd, Dy, Tb, Ho, Er, and Sc. The remaining ternary oxide is Li₂HfO₃, which belongs to the set of competing phases for the garnet Li₇La₃Hf₂O₁₂. Within the 21 ternary nitrides, six are members of Li_(x)MN₄, where x=5, 6, or 7 and M is a transition metal including Ta, Nb, W, V, Re, and Mo. These nitride compounds are similar in composition to Li₃N, which is known to have good Li conductivity. However, these compounds have larger bandgaps than Li₃N, which may improve their ability to block electron transfer. And, unlike Li₃N, many of these compounds exhibit stable equilibrium with oxide solid electrolytes.

Tables 3-10 list coatings for Li metal anodes. Tables 3-9 list binary and ternary coatings containing F, O, Cl, N, Br, S, and C anions, respectively. Table 10 lists quaternary coatings, which include N, O, and C anions. Electronic bandgaps and stabilities are reported in eV. Stabilities are calculated with respect to the nearest-energy set of competing phases. Space group and prototype structure are also listed.

TABLE 3 Fluoride binary and ternary coatings for Li metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds LiF 9.56 −1.050 LiF₂—Li₃F₂ Fm3m B1 EuF₂ 7.94 −0.925 Eu₂F₃—EuF₃ Fm3m CaF₂ SrF₂ 7.43 −1.232 SrF—SrF₃ Fm3m CaF₂ CaF₂ 7.41 −0.965 CaF₃—Ca₂F₃ R3m None YbF₂ 7.31 −1.287 YbF₃—YbF P4₂/mnm C4

TABLE 4 Oxide binary and ternary coatings for Li metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds BeO 7.90 −1.584 Be—Be₂O₃ P6₃mc B4 Li₂O 5.08 −0.657 LiO—Li₃O R3m None Y₂O₃ 4.37 −0.823 YO₂—Y₄O₅ Ia3 Mn₂O₃ Lu₂O₃ 4.22 −1.056 Lu₄O₅—O₂ Ia3 Mn₂O₃ Dy₂O₃ 4.17 −0.989 Dy₄O₅—O₂ Ia3 Mn₂O₃ Tm₂O₃ 4.16 −0.859 TmO₂—Tm₄O₅ I2₁₃ Sm₂O₃ Ho₂O₃ 4.14 −1.011 Ho₄O₅—O₂ Ia3 Mn₂O₃ Er₂O₃ 4.12 −1.016 Er₄O₅—O₂ Ia3 Mn₂O₃ Gd₂O₃ 4.08 −0.969 Gd₄O₅—O₂ Ia3 Mn₂O₃ Nd₂O₃ 4.05 −0.571 NdO₂—NdO Ia3 Mn₂O₃ Sm₂O₃ 3.98 −0.824 Sm₄O₅—SmO₂ Ia3 Mn₂O₃ Pr₂O₃ 3.91 −0.419 Pr₇O₁₂—PrO Ia3 Mn₂O₃ La₂O₃ 3.81 −1.134 LaO—LaO₃ Ia3 Mn₂O₃ CaO 3.75 −1.134 Ca₂O₃—Ca₂O Fm3m B1 YbO 3.52 −0.950 Yb₄O₅—Yb₃O₂ Fm3m B1 EuO 2.81 −0.797 Eu₂O—Eu₃O₄ Fm3m B1 Ternary Lithium-Containing Compounds LiGdO₂ 4.90 −0.004 Li₂O—Gd₂O₃ Pnma SrZnO₂ Li₂HfO₃ 4.86 −0.096 Li₂O—Li₈Hf₄O₁₁—Li₆Hf₄O₁₁ C2/m None LiDyO₂ 4.83 −0.012 Li₂O—Dy₂O₃ Pnma SrZnO₂ LiTbO₂ 4.83 −0.008 Li₂O—Tb₂O₃ Pnma SrZnO₂ LiHoO₂ 4.51 −0.001 Li₂O—Ho₂O₃ P2₁/c YLiO₂ LiErO₂ 4.51 −0.011 Li₂O—Er₂O₃ P2₁/c YLiO₂ LiScO₂ 4.32 −0.090 Li₂O—Sc₂O₃ I4₁/amd LiFeO₂- alpha

TABLE 5 Chloride binary and ternary coatings for Li metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds LiCl 6.25 −0.772 Li₃Cl₂—LiCl₂ F4 ₃m B3 BaCl₂ 5.69 −0.648 BaCl₃—Ba₂Cl₃ Fm3m CaF₂ YbCl₂ 5.63 −0.250 Yb₆Cl₁₃—Yb P4₂/mnm C4 SrCl₂ 5.53 −0.962 SrCl—SrCl₃ Fm3m CaF₂ KCl 5.30 −0.732 KCl₂—K₃Cl₂ Fm3m B1 EuCl₂ 5.19 −0.837 EuCl—EuCl₃ Pnma PbCl₂ NaCl 5.18 −0.727 NaCl₂—Na₃Cl₂ Fm3m B1 CsCl 5.08 −0.629 Cs₃Cl₂—CsCl₂ Fm3m B1 RbCl 4.98 −0.715 Rb₃Cl₂—Cl₂ R3m L1₁ Ternary Lithium-Containing Compounds Li₄NCl 2.02 −0.007 Li₃N—Li₅NCl₂ R3m None

TABLE 6 Nitride binary and ternary coatings for Li metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds AlN 4.34 −1.275 Al₃N—N₂ P6₃mc B4 Be₃N₂ 3.52 −0.710 Be₂N—N₂ Ia3 Mn₂O₃ LaN 1.29 −0.647 La₂N—N₂ P6₃mc B4 Li₃N 1.22 −0.319 Li—N₂ P6/mmm Li₃N Ternary Lithium-Containing Compounds Li₂CN₂ 4.11 −0.404 Li₃N—LiCN—N₂ I4/mmm None Li₂SiN₂ 4.07 −0.131 Li₃N—LiSi₂N₃ Pbca None Li₃BN₂ 3.67 −0.176 Li₃N—BN P2₁/c Na₃BN₂ Li₇TaN₄ 3.51 −0.079 Li₃N—Li₄TaN₃ Pa3 Li₇TaN₄ Li₇NbN₄ 3.51 −0.278 Li₃N—Nb₅N₆—N₂ Pa3 Li₇TaN₄ Li₆WN₄ 3.38 −0.485 Li₃N—W—N₂ P4₂/nmc Li₆ZnO₄ Li₇VN₄ 3.32 −0.293 Li₃N—VN—N₂ Pa3 Li₇TaN₄ LiBeN 3.00 −0.115 Li₃N—Be₃N₂ P2₁/c None Li₅ReN₄ 2.92 −0.365 Li₃N—Re—N₂ Pmmn Li₅AlO₄ Li₆MoN₄ 2.78 −0.325 Li₃N—LiMoN₂—N₂ P4₂/nmc Li₆ZnO₄ Li₈TeN₂ 2.63 −0.025 Li₃N—Li₂Te I4₁md None LiMgN 2.56 −0.058 Li₃N—Mg₃N₂ Pnma None Li₅Br₂N 2.46 −0.008 LiBr—Li₁₀BrN₃ Immm None Li₃ScN₂ 2.44 −0.049 Li₃N—ScN Ia3 AlLi₃N₂ Li₄NCl 2.02 −0.007 Li₃N—Li₅NCl₂ R3m None Li₄HN 1.98 −0.002 Li₃N—LiH I4₁/a CaWO₄ Li₈SeN₂ 1.89 −0.001 Li₃N—Li₂Se I4₁md None Li₂ZrN₂ 1.73 −0.221 Li₃N—Zr₃N₄ P3m1 La₂O₃ LiCaN 1.64 −0.049 Li₃N—Ca₃N₂ Pnma None Li₁₀BrN₃ 1.54 −0.005 Li₃N—Li₅Br₂N P6m2 None SrLi₄N₂ 1.10 −0.016 Li₃N—SrLiN I4₁/amd Li₄SrN₂

TABLE 7 Bromide binary and ternary coatings for Li metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds LiBr 5.15 −0.673 LiBr₂—Li₃Br₂ F4 ₃m B3 YbBr₂ 4.80 −0.783 YbBr₃—YbBr Pnnm None SrBr₂ 4.72 −0.827 SrBr₃—SrBr Pnma PbCl₂ BaBr₂ 4.48 −0.557 Ba₂Br₃—BaBr₃ Pnma PbCl₂ KBr 4.45 −0.622 K₃Br₂—KBr₂ Fm3m NaCl RbBr 4.42 −0.613 Rb₃Br₂—RbBr₂ Fm3m B1 CsBr 4.41 −0.543 CsBr₃—Cs₃Br₂ Fm3m B1 EuBr₂ 4.40 −0.812 EuBr—EuBr₃ P4/n SrBr₂ NaBr 4.36 −0.639 NaBr₃—Na₃Br₂ Fm3m B1 Ternary Lithium-Containing Compounds Li₅Br₂N 2.46 −0.008 LiBr—Li₁₀BrN₃ Immm None Li₁₀BrN₃ 1.54 −0.005 Li₃N—Li₅Br₂N P6m2 None

TABLE 8 Sulfide binary and ternary coatings for Li metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds Li₂S 3.66 −0.561 Li₃S—LiS Fm3m None SrS 2.57 −0.666 SrS₂—Sr₃S₂ Fm3m B1 CaS 2.50 −0.988 Ca₂S—Ca₂S₃ Fm3m B1 YbS 2.33 −0.431 Yb₃S₂—Yb₇S₈ Fm3m None BaS 2.24 −0.594 Ba₂S—Ba₂S₃ Fm3m B1 EuS 2.07 −0.701 Eu₂S—Eu₃S₄ Fm3m NaCl

TABLE 9 Carbide binary and ternary coatings for Li metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds Be₂C 1.41 −0.234 Be—C Fm3m CaF₂ Ternary Lithium-Containing Compounds Li₂CN₂ 4.11 −0.404 Li₃N—LiCN—N₂ I4/mmm None LiBC 1.22 −0.270 LiB₆C—C—Li P6₃/mmc KZnAs

TABLE 10 Quaternary coatings for lithium metal anodes. Band Competing Space Gap Stability Phases Group Prototype Oxide Compounds Li₇La₃Hf₂O₁₂ 4.68 −0.006 Li₂O—Li₂HfO₃—La₂O₃ I4₁/acd None Li1₆Nb₂N₈O 3.73 −0.004 Li₂O—Li₇NbN₄ R3 Li₁₆Ta₂N₈O Li1₆Ta₂N₈O 3.53 −0.005 Li₂O—Li₇TaN₄ R3 Li₁₆Ta₂N₈O LiSmEu₂O₄ 3.05 −0.006 Li₂O—EuO—Sm₂O₃ Pnma None Nitride Compounds Li₁₆Nb₂N₈O 3.73 −0.004 Li₂O—Li₇NbN₄ R3 Li₁₆Ta₂N₈O Li₁₆Ta₂N₈O 3.53 −0.005 Li₂O—Li₇TaN₄ R3 Li₁₆Ta₂N₈O Li₅La₅Si₄N₁₂ 2.68 −0.046 LaN—La₅Si₃N₉—Li₂SiN₂ P4b2 None Li₄Ca₃Si₂N₆ 2.58 −0.054 Li₂SiN₂—LiCaN—Ca₅Si₂N₆ C2/m None Sr₄LiB₃N₆ 2.47 −0.241 BN—Sr₂N—Li₃BN₂—SrN Im3m Sr₉B₆N₁₂ Li₅Ce₅Si₄N₁₂ 2.43 −0.039 Li₂SiN₂—CeN—Ce₃Si₆N₁₁ P4b2 None LiEu₄B₃N₆ 2.40 −0.058 Li₃BN₂—Eu₃B₂N₄ Im3m Sr₉B₆N₁₂ LiCa₄B₃N₆ 2.40 −0.081 Ca₃BN₃—Li₃BN₂—BN Im3m Sr₉B₆N₁₂ Sr₃Li₄Si₂N₆ 2.22 −0.062 SrLiN—SrLi₂Si₂N₄ C2/m None SrLi₂CrN₃ 1.09 −0.265 Li₃N—Sr₃CrN₃—CrN—N₂ Pbca TeCl₂SSeN₂ Carbide Compounds LiCa₂HC₃ 1.50 −0.140 Ca—CaH₂—Li₂Ca—C P4/mbm None

Tables 11-18 list coatings for Na metal anodes. Tables 11-17 list binary and ternary coatings containing F, O, Cl, N, Br, S, and C anions, respectively. Table 18 lists quaternary coatings, which include N and O anions. Electronic bandgaps and stabilities are reported in eV. Stabilities are calculated with respect to the nearest-energy set of competing phases. Space group and prototype structure are also listed.

TABLE 11 Fluoride binary and ternary coatings for Na metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds LiF 9.56 −1.050 LiF₂—Li₃F₂ Fm3m B1 EuF₂ 7.94 −0.925 Eu₂F₃—EuF₃ Fm3m CaF₂ SrF₂ 7.43 −1.232 SrF—SrF₃ Fm3m CaF₂ CaF₂ 7.41 −0.965 CaF₃—Ca₂F₃ R3m None YbF₂ 7.31 −1.287 YbF₃—YbF P4₂/mnm C4 BaF₂ 7.05 −0.846 BaF₃—Ba₂F₃ Fm3m None NaF 6.65 −0.908 Na₃F₂—NaF₂ Fm3m B1

TABLE 12 Oxide binary and ternary coatings for Na metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds BeO 7.90 −1.584 Be—Be₂O₃ P6₃mc B4 Li₂O 5.08 −0.657 LiO—Li₃O R3m None MgO 4.97 −1.010 Mg₂O—Mg₄O₅ Fm3m B1 Y₂O₃ 4.37 −0.823 Y₄O₅—YO₂ Ia3 Mn₂O₃ HfO₂ 4.29 −0.784 Hf₂O₃—Hf₂O₅ P2₁/c ZrO₂ Lu₂O₃ 4.22 −1.056 Lu₄O₅—O₂ Ia3 Mn₂O₃ Dy₂O₃ 4.17 −0.989 Dy₄O₅—O₂ Ia3 Mn₂O₃ Tm₂O₃ 4.16 −0.859 TmO₂—Tm₄O₅ I2₁₃ Sm₂O₃ Ho₂O₃ 4.14 −1.011 Ho₄O₅—O₂ Ia3 Mn₂O₃ Sc₂O₃ 4.12 −0.840 ScO₂—Sc₄O₅ Ia3 Mn₂O₃ Er₂O₃ 4.12 −1.016 Er₄O₅—O₂ Ia3 Mn₂O₃ Tb₂O₃ 4.09 −0.488 TbO—Tb₇O₁₂ Ia3 Mn₂O₃ Gd₂O₃ 4.08 −0.969 Gd₄O₅—O₂ Ia3 Mn₂O₃ Nd₂O₃ 4.05 −0.571 NdO₂—NdO Ia3 Mn₂O₃ Sm₂O₃ 3.98 −0.824 Sm₄O₅—SmO₂ Ia3 Mn₂O₃ Pr₂O₃ 3.91 −0.419 Pr₇O₁₂—PrO Ia3 Mn₂O₃ Ce₂O₃ 3.81 −0.409 Ce₇O₁₂—CeO Ia3 Mn₂O₃ La₂O₃ 3.81 −1.134 LaO—LaO₃ Ia3 Mn₂O₃ CaO 3.75 −1.134 Ca₂O₃—Ca₂O Fm3m B1 SrO 3.52 −0.801 Sr₃O₂—Sr₄O₃ Fm3m B1 YbO 3.52 −0.950 Yb₃O₂—Yb₄O₅ Fm3m B1 EuO 2.81 −0.797 Eu₂O—Eu₃O₄ Fm3m B1 Na₂O 2.22 −0.406 NaO—Na₃O Fm3m CaF₂ BaO 2.10 −0.710 Ba₄O₅—Ba₂O Fm3m B1 Ternary Sodium-Containing Compounds Na₂ZrO₃ 4.51 −0.110 Na₈Zr₄O₁₁—Na₆Zr₂O₇—ZrO₂ C2/m None NaYO₂ 4.49 −0.099 Na₂O—Y₂O₃ C2/c None NaErO₂ 4.44 −0.115 Na₂O—Er₂O₃ C2/c NaErO₂ NaTbO₂ 4.17 −0.103 Na₂O—Tb₂O₃ I4₁/amd LiFeO₂- alpha NaGdO₂ 4.13 −0.102 Na₂O—Gd₂O₃ I4₁/amd LiFeO₂- alpha NaAlO₂ 4.13 −0.117 Na₇Al₃O₈—Al₂O₃ Pna2₁ NaFeO₂ Na₆Be₈O₁₁ 3.95 −0.002 Na₂BeO₂—BeO P1 None NaNdO₂ 3.72 −0.089 Na₂O—Nd₂O₃ I4₁/amd LiFeO₂- alpha NaScO₂ 3.70 −0.093 Na₂O—Sc₂O₃ I4₁/amd None Na₄WO₅ 3.67 −0.100 Na₂O—Na₂WO₄ P1 Li₄TeO₅ Na₄SiO₄ 3.60 −0.091 Na₂SiO₃—Na₈SiO₆ P1 None NaPrO₂ 3.60 −0.082 Na₂O—Pr₂O₃ I4₁/amd LiFeO₂- alpha Na₄TiO₄ 3.59 −0.112 Na₂O—Na₂TiO₃ P1 Na₄SiO₄ Na₃BO₃ 3.33 −0.072 Na₂O—Na₄B₂O₅ P2₁/c None Na₂BeO₂ 3.11 −0.045 Na₂O—Na₆Be₈O₁₁ P2₁ None Na₇Al₃O₈ 2.98 −0.007 NaAlO₂—Na₁₇Al₅O₁₆ P1 None Na₅TaO₅ 2.87 −0.148 Na₂O—NaTaO₃ C2/c Na₅NbO₅ Na₅NbO₅ 2.81 −0.158 Na₂O—NaNbO₃ C2/c Na₅NbO₅ Na₅AlO₄ 2.66 −0.005 Na₂O—Na₁₇Al₅O₁₆ Pmmn None Na₁₇Al₅O₁₆ 2.56 −0.007 Na₅AlO₄—Na₇Al₃O₈ Cm None Na₄I₂O 2.44 −0.030 Na₂O—NaI I4/mmm K₂MgF₄ Na₅GaO₄ 2.40 −0.040 Na₂O—Na₃₉Ga₈O₃₂—NaGa₄ Pbca None Na₃ClO 2.25 −0.003 NaCl Pm3m CaTiO₃ Na₂Hf₂O₅ 2.17 −0.011 Na₂O—HfO₂ P4/mmm defect_perovskite Na₄Br₂O 2.14 −0.019 NaBr I4/mmm K₂MgF₄ NaNbO₂ 1.53 −0.137 NaNbO₃—Nb—Na₅NbO₅ P6₃/mmc None

TABLE 13 Chloride coatings for sodium metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds YbCl₂ 5.63 −0.250 Yb₆Cl₁₃—Yb P4₂/mnm C4 EuCl₂ 5.19 −0.837 EuCl—EuCl₃ Pnma PbCl₂ NaCl 5.18 −0.727 NaCl₂—Na₃Cl₂ Fm3m B1 CsCl 5.08 −0.629 Cs₃Cl₂—CsCl₂ Fm3m B1 RbCl 4.98 −0.715 Rb₃Cl₂—Cl₂ R3m L1₁ Ternary Sodium-Containing Compounds Na₃ClO 2.25 −0.003 NaCl Pm3m CaTiO₃

TABLE 14 Nitride binary and ternary coatings for Na metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds BN 4.38 −1.071 B₁₃N₂—N₂ P6₃/mmc BN AlN 4.34 −1.275 Al₃N—N₂ P6₃mc B4 Be₃N₂ 3.52 −0.710 Be₂N—N₂ Ia3 Mn₂O₃ GaN 1.99 −0.382 Ga—N₂ P6₃mc B4 Mg₃N₂ 1.78 −0.351 Mg₂N—N₂ Ia3 Mn₂O₃ LaN 1.29 −0.647 La₂N—N₂ P6₃mc B4 Ca₃N₂ 1.26 −0.091 Ca₂N—N₂ Ia3 Mn₂O₃ Li₃N 1.22 −0.319 Li—N₂ P6/mmm Li₃N Hf₃N₄ 1.17 −0.071 HfN—N₂ I4 ₃d Th₃P₄ Zr₃N₄ 1.04 −0.009 ZrN—N₂ Pnma None Ternary Sodium-Containing Compounds NaPN₂ 4.87 −0.259 NaP₄N₇—Na₃P—N₂ I4 ₂d KCoO₂ NaSi₂N₃ 4.48 −0.186 Na—Si₃N₄—N₂ Cmc2₁ Na₂SiO₃ Na₂CN₂ 3.35 −0.337 Na—NaCN—N₂ C2/m K₂ Na₄ReN₃ 2.48 −0.255 Na—Re—N₂ Cc Na₄FeO₃ NaH₂N 2.13 −0.122 NaH—H₃N—N₂ Fddd NaNH₂ Na₃WN₃ 1.85 −0.429 Na—W—N₂ Cc Na₃MoN₃ Na₃BN₂ 1.85 −0.114 Na—BN—N₂ P2₁/c Na₃BN₂ Na₃MoN₃ 1.58 −0.280 Na—MoN—N₂ Cc Na₃MoN₃ NaTaN₂ 1.51 −0.188 Na—NaTa₃N₅—N₂ R3m NaCrS₂

TABLE 15 Bromide binary and ternary coatings for Na metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds KBr 4.45 −0.622 K₃Br₂—KBr₂ Fm3m NaCl RbBr 4.42 −0.613 Rb₃Br₂—RbBr₂ Fm3m B1 CsBr 4.41 −0.543 CsBr₃—Cs₃Br₂ Fm3m B1 EuBr₂ 4.40 −0.812 EuBr—EuBr₃ P4/n SrBr₂ NaBr 4.36 −0.639 NaBr₃—Na₃Br₂ Fm3m B1 Ternary Sodium-Containing Compounds Na₄Br₂O 2.14 −0.019 NaBr I4/mmm K₂MgF₄

TABLE 16 Sulfide binary and ternary coatings for Na metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds Li₂S 3.66 −0.561 Li₃S—LiS Fm3m None Na₂S 2.63 −0.377 Na₃S—NaS Fm3m CaF₂ SrS 2.57 −0.666 SrS₂—Sr₃S₂ Fm3m B1 CaS 2.50 −0.988 Ca₂S—Ca₂S₃ Fm3m B1 YbS 2.33 −0.431 Yb₃S₂—Yb₇S₈ Fm3m None BaS 2.24 −0.594 Ba₂S—Ba₂S₃ Fm3m B1 EuS 2.07 −0.701 Eu₂S—Eu₃S₄ Fm3m NaCl Ternary Sodium-Containing Compounds NaLiS 3.40 −0.005 Li₂S P4/nmm Cu₂Sb NaLuS₂ 2.55 −0.153 Na₂S—Lu₂S₃ R3m NaCrS₂ NaErS₂ 2.47 −0.159 Na₂S—Er₂S₃ R3m NaCrS₂ NaHoS₂ 2.42 −0.154 Na₂S—Ho₂S₃ R3m NaCrS₂ NaYS₂ 2.40 −0.152 Na₂S—Y₂S₃ R3m NaCrS₂ NaTmS₂ 2.39 −0.153 Na₂S—Tm₂S₃ R3m NaCrS₂

TABLE 17 Carbide binary and ternary coatings for Na metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds SiC 2.15 −0.209 C—Si P6₃mc SiC Al₄C₃ 1.47 −0.098 C—Al R3m None Be₂C 1.41 −0.234 Be—C Fm3m CaF₂ Ternary Sodium-Containing Compounds Na₂CN₂ 3.35 −0.337 Na—NaCN—N₂ C2/m K₂

TABLE 18 Quaternary coatings for sodium metal anodes. Band Competing Space Gap Stability Phases Group Prototype Oxide Compounds NaLi₂PO₄ 5.65 −0.054 Na₂O—Na₄P₂O₇—Li₃PO₄ Pnma Li₃PO₄ NaLi₃SiO₄ 5.28 −0.007 Na₄SiO₄—Li₄SiO₄ I4₁/a None Na₃Ca₂TaO₆ 4.39 −0.073 NaTaO₃—CaO—Na₅TaO₅ Fddd None Na₂MgSiO₄ 4.15 −0.018 MgO—Na₂SiO₃ Pna2₁ Na₂ZnSiO₄ NaLa₂TaO₆ 4.12 −0.017 La₃TaO₇—Na₅TaO₅—NaTaO₃ P2₁/c Na₃AlF₆ NaSr₃TaO₆ 4.11 −0.056 Na₅TaO₅—Sr₂Ta₂O₇—SrO R3c K₄CdCl₆ NaSrBO₃ 4.10 −0.020 Na₃BO₃—Sr₃B₂O₆ P2₁/c None BaNaBO₃ 4.00 −0.171 NaBO₂—BaO C2/m Na₂CO₃ Ba₃NaTaO₆ 3.63 −0.061 Na₅TaO₅—Ba₄Ta₂O₉—BaO R3c K₄CdCl₆ Na₅WNO₄ 3.31 −0.012 Na₂O—Na₄WN₂O₂—Na₄WO₅ CmcC2₁ None Ba₃NaNbO₆ 3.26 −0.067 Na₅NbO₅—BaO—Ba₃Nb₂O₈ R3c K₄CdCl₆ Na₄MoN₂O₂ 2.58 −0.040 Na₃MoN₃—Na₅MoNO₄ P1 Na₄WO₂N₂ Na₄WN₂O₂ 2.21 −0.025 Na₃WN₃—Na₅WNO₄ P1 Na₄WO₂N₂ Nitride Compounds Na₅WNO₄ 3.31 −0.012 Na₂O—Na₄WN₂O₂—Na₄WO₅ Cmc2₁ None NaLi₃H₈N₄ 2.97 −0.007 NaH₂N—LiH₂N I4 LiNH₂ Na₄MoN₂O₂ 2.58 −0.040 Na₃MoN₃—Na₅MoNO₄ P3 Na₄WO₂N₂ NaSr₄B₃N₆ 2.22 −0.256 BN—Sr₂N—Na₃BN₂—SrN Im3m SrgB₆N₁₂ Na₄WN₂O₂ 2.21 −0.025 Na₃WN₃—Na₅WNO₄ P1 Na₄WO₂N₂ Ba₄NaB₃N₆ 2.18 −0.027 Ba₃B₂N₄—Na₃BN₂ Im3m Sr₉B₆N₁₂

For Na metal anodes, Tables 11-17 list the binary and ternary compounds that passed the screens containing F, O, Cl, N, Br, S, and C anions respectively. Table 18 lists all quaternary compounds for lithium metal anodes, which contained only O and N anions. Na solid electrolytes for room temperature batteries have been studied less than Li solid electrolytes due to the relatively modest performance of Na solid electrolytes and electrodes. The most famous Na solid electrolyte is Na-beta alumina (Na-β″-Al₂O₃), which has a composition given by (Na₂O)_(1+x)(Al₂O₃)₁₁, where x ranges from 0 to 0.57. Na-beta alumina is not in the OQMD dataset. The compound that is nearest in composition to Na-beta alumina in the OQMD is Al₂O₃, which did not pass the screens. However, four ternary Na—Al—O compounds were identified that passed the screens, including NaAlO₂, Na₇Al₃O₈, Na₅AlO₄, and Na₁₇Al₁₅O₁₆. This finding of Na—Al—O coatings for Na anodes differed from the finding for Li anodes, where no ternary Li—Al—O compounds passed the screens.

The set of oxide coatings for Na metal anodes included 63 compounds comprising 24 binaries, 26 ternaries, and 13 quaternaries, making it the largest set among the anode/anion pairs that were considered. Fourteen compounds were identified with the formula R₂O₃, where R is a rare earth including Y, Lu, Dy, Tm, Ho, Sc, Er, Tb, Gd, Nd, Sm, Pr, Ce, and La. Seven ternary oxides were also identified with the formula NaRO₂, where R is a rare earth including Y, Er, Tb, Gd, Nd, Sc, and Pr. Six ternary sulfides were identified for Na anodes, including five compounds with the formula NaRS₂, where R is a rare earth including Lu, Er, Ho, Y, and Tm. Whereas, for Li anodes, no ternary sulfides were identified.

Tables 19-25 list binary and ternary coatings for Mg anodes containing F, O, Cl, N, Br, S, and C anions, respectively. No quaternary coatings were identified for Mg anodes. Electronic bandgaps and stabilities are reported in eV. Stabilities are calculated with respect to the nearest-energy set of competing phases. Space group and prototype structure are also listed.

TABLE 19 Fluoride binary and ternary coatings for Mg metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds LiF 9.56 −1.050 LiF₂—Li₃F₂ Fm3m B1 SmF₃ 8.38 −1.680 SmF₂—F₂ Pnma YF₃ HoF₃ 8.32 −1.713 HoF₂—F₂ Pnma YF₃ ErF₃ 8.31 −2.450 Er₂F₃—F₂ Pnma YF₃ EuF₂ 7.94 −0.925 Eu₂F₃—EuF₃ Fm3m CaF₂ MgF₂ 7.64 −1.487 MgF₃—MgF P4₂/mnm TiO₂ SrF₂ 7.43 −1.232 SrF₃—SrF Fm3m CaF₂ CaF₂ 7.41 −0.965 Ca₂F₃—CaF₃ R3m None YbF₂ 7.31 −1.287 YbF₃—YbF P4₂/mnm C4 BaF₂ 7.05 −0.846 BaF₃—Ba₂F₃ Fm3m None NaF 6.65 −0.908 Na₃F₂—NaF₂ Fm3m B1 Ternary Magnesium-Containing Compounds KMgF₃ 7.85 −0.038 K₂MgF₄—MgF₂ Pm3m CaTiO₃ NaMgF₃ 7.51 −0.025 NaF—MgF₂ Pnma GdFeO₃ RbMgF₃ 7.47 −0.020 Rb₂MgF₄—MgF₂ P6₃/mmc BaFeO₂ + x Cs₄Mg₃F₁₀ 7.00 −0.041 CsF—MgF₂ Cmca Sr₄Mn₃O₁₀ Mg₃NF₃ 4.23 −0.011 Mg₂NF—MgF₂ Pm3m U₄S₃

TABLE 20 Oxide binary and ternary coatings for Mg metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds BeO 7.90 −1.584 Be—Be₂O₃ P6₃mc B4 MgO 4.97 −1.010 Mg₂O—Mg₄O₅ Fm3m B1 Y₂O₃ 4.37 −0.823 Y₄O₅—YO₂ Ia3 Mn₂O₃ Lu₂O3 4.22 −1.056 Lu₄O₅—O₂ Ia3 Mn₂O₃ Dy₂O3 4.17 −0.989 Dy₄O₅—O₂ Ia3 Mn₂O₃ Tm₂O₃ 4.16 −0.859 TmO₂—Tm₄O₅ I2₁₃ Sm₂O₃ Ho₂O₃ 4.14 −1.011 Ho₄O₅—O₂ Ia3 Mn₂O3 Sc₂O₃ 4.12 −0.840 ScO₂—Sc₄O₅ Ia3 Mn₂O₃ Er₂O₃ 4.12 −1.016 Er₄O₅—O₂ Ia3 Mn₂O₃ Tb₂O₃ 4.09 −0.488 TbO—Tb₇O₁₂ Ia3 Mn₂O₃ Gd₂O₃ 4.08 −0.969 Gd₄O₅—O₂ Ia3 Mn₂O₃ CaO 3.75 −1.134 Ca₂O₃—Ca₂O Fm3m B1 YbO 3.52 −0.950 Yb₄O₅—Yb₃O₂ Fm3m B1 EuO 2.81 −0.797 Eu₂O—Eu₃O₄ Fm3m B1

TABLE 21 Chloride binary and ternary coatings for Mg metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds LiCl 6.25 −0.772 LiCl₂—Li₃Cl₂ F4 ₃m B3 BaCl₂ 5.69 −0.648 BaCl₃—Ba₂Cl₃ Fm3m CaF₂ YbCl₂ 5.63 −0.250 Yb₆Cl₁₃—Yb P4₂/mnm C4 MgCl₂ 5.62 −0.883 MgCl—MgCl₃ R3m CdCl₂ SrCl₂ 5.53 −0.962 SrCl—SrCl₃ Fm3m CaF₂ CaCl₂ 5.48 −0.723 Ca₂Cl₃—CaCl₃ P4₂/mnm TiO₂ KCl 5.30 −0.732 KCl₂—K₃Cl₂ Fm3m B1 EuCl₂ 5.19 −0.837 EuCl—EuCl₃ Pnma PbCl₂ NaCl 5.18 −0.727 NaCl₂—Na₃Cl₂ Fm3m B1 CsCl 5.08 −0.629 Cs₃Cl₂—CsCl₂ Fm3m B1 RbCl 4.98 −0.715 Rb₃Cl₂—Cl₂ R3m L1₁ TmCl₃ 4.92 −0.857 TmCl₂—Cl₂ R3c FeF₃ YCl₃ 4.77 −0.834 YCl₂—Cl₂ C2/m RhBr₃ TbCl₃ 4.74 −0.822 TbCl₂—Cl₂ P4₂/mnm None CeCl₃ 4.71 −1.252 Ce₂Cl₃—Cl₂ P2₁/m UCl₃ PrCl₃ 4.46 −0.813 PrCl₂—Cl₂ P2₁/m UCl₃ NdCl₃ 4.43 −0.807 NdCl₂—Cl₂ P2₁/m UCl₃ GdCl₃ 4.37 −0.799 GdCl₂—Cl₂ P6₃/m UCl₃ DyCl₃ 3.75 −0.818 DyCl₂—Cl₂ Cmcm NdBr₃ LaCl₃ 3.74 −0.855 LaCl₂—Cl₂ P6₃/m UCl₃ LuCl₃ 3.19 −0.791 LuCl₂—Cl₂ P6₃/mmc DO₁₉ Ternary Magnesium-Containing Compounds CsMgCl₃ 5.34 −0.031 Cs₂MgCl₄—MgCl₂ Cmcm BaNiO₃ Cs₂MgCl₄ 5.16 0.000 CsMgCl₃—CsCl Pnma Cs₂CuCl₄ RbMgCl₃ 5.04 −0.028 RbCl—MgCl₂ P6₃/mmc None K₂MgCl₄ 4.99 −0.003 KCl—MgCl₂ I4/mmm K₂MgF₄

TABLE 22 Nitride binary and ternary coatings for Mg metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds BN 4.38 −1.071 B₁₃N₂—N₂ P6₃/mmc BN AlN 4.34 −1.275 Al₃N—N₂ P6₃mc B4 Be₃N₂ 3.52 −0.710 Be₂N—N₂ Ia3 Mn₂O₃ Mg₃N₂ 1.78 −0.351 Mg₂N—N₂ Ia3 Mn₂O₃ Ternary Magnesium-Containing Compounds MgSiN₂ 4.29 −0.224 Mg₃N₂—Si₃N₄ Pna2₁ NaFeO₂ MS₃NF₃ 4.23 −0.011 Mg₂NF—MgF₂ Pm3m U₄S₃ MgBe₂N₂ 4.16 −0.083 Mg₃N₂—Be₃N₂ P3m1 La₂O₃ MgB₉N 1.82 −0.064 B-MgB₇—BN R3m None

TABLE 23 Bromide binary and ternary coatings for Mg metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds LiBr 5.15 −0.673 LiBr₂—Li₃Br₂ F4 ₃m B3 YbBr₂ 4.80 −0.783 YbBr₃—YbBr Pnnm None SrBr₂ 4.72 −0.827 SrBr₃—SrBr Pnma PbCl₂ CaBr₂ 4.68 −0.898 CaBr₃—CaBr Pnnm CaCl₂ MgBr₂ 4.63 −0.770 MgBr—MgBr₃ P3m1 CdI₂/ Mg(OH)₂ BaBr₂ 4.48 −0.557 Ba₂Br₃—BaBr₃ Pnma PbCl₂ KBr 4.45 −0.622 K₃Br₂—KBr₂ Fm3m NaCl RbBr 4.42 −0.613 Rb₃Br₂—RbBr₂ Fm3m B1 CsBr 4.41 −0.543 CsBr₃—Cs₃Br₂ Fm3m B1 EuBr₂ 4.40 −0.812 EuBr₃—EuBr P4/n SrBr₂ NaBr 4.36 −0.639 NaBr₃—Na₃Br₂ Fm3m B1 GdBr₃ 3.80 −0.731 GdBr₂—Br₂ C2/m RhBr₃ PrBr₃ 3.57 −0.292 Pr₂Br₅—Br₂ P6₃/m UCl₃ CeBr₃ 3.55 −0.299 Ce₂Br₅—Br₂ P2₁/m UCl₃ LaBr₃ 3.10 −0.312 La₂Br₅—Br₂ P6₃/m UCl₃ SmBr₃ 2.87 −0.687 SmBr₂—Br₂ Cmcm NdBr₃ NdBr₃ 2.85 −0.679 NdBr₂—Br₂ Cmcm NdBr₃ ErBr₃ 2.27 −0.653 ErBr₂—Br₂ P6₃/mmc DO₁₉ Ternary Magnesium-Containing Compounds CsMgBr₃ 4.23 −0.041 MgBr₂—CsBr Cmcm BaNiO₃

TABLE 24 Sulfur binary and ternary coatings for Mg metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds Li₂S 3.66 −0.561 Li₃S—LiS Fm3m None MgS 2.85 −0.608 MgS₂—Mg₂S R3m L1₁ Na₂S 2.63 −0.377 Na₃S—NaS Fm3m CaF₂ SrS 2.57 −0.666 SrS₂—Sr₃S₂ Fm3m B1 CaS 2.50 −0.988 Ca₂S₃—Ca₂S Fm3m B1 K₂S 2.44 −0.339 K₃S—KS Fm3m CaF₂ YbS 2.33 −0.431 Yb₃S₂—Yb₇S₈ Fm3m None BaS 2.24 −0.594 Ba₂S—Ba₂S₃ Fm3m B1 Cs₂S 2.21 −0.240 Cs₃S—CsS Pnma None Rb₂S 2.21 −0.297 RbS—Rb₃S Fm3m CaF₂ EuS 2.07 −0.701 Eu₃S₄—Eu₂S Fm3m NaCl Ternary Magnesium-Containing Compounds Lu₂MgS₄ 2.13 −0.011 MgS—Lu₂S₃ Fd3m Al₂MgO₄

TABLE 25 Carbide binary and ternary coatings for Mg metal anodes. Band Competing Space Gap Stability Phases Group Prototype Binary Compounds Al₄C₃ 1.47 −0.098 C—Al R3m None Be₂C 1.41 −0.234 Be—C Fm3m CaF₂ Ternary Magnesium-Containing Compounds MgAl₂C₂ 1.90 −0.002 Mg—Al₄C₃—C P3m1 La₂O₃ MgB₂C₂ 1.16 −0.070 Mg—C—MgB₁₂C₂ Cmca None

For Mg metal anodes, Tables 19-25 list the binary and ternary compounds that passed the screens containing F, O, Cl, N, Br, S, and C anions respectively. No quaternary compounds passed the screens for Mg anodes. Five ternary fluoride coatings were identified for Mg anodes, whereas no ternary fluorides passed the screens for Li or Na anodes. Nine coatings were identified with the formula R₂O₃, where R is a rare earth including Y, Lu, Dy, Tm, Ho, Sc, Er, Tb, and Gd. Ten coatings were identified with the formula RCl₃, where R is a rare earth including Tm, Y, Tb, Ce, Pr, Nd, Gd, Dy, La, and Lu. One ternary sulfide was identified, Lu₂MgS₄.

Each compound that passed the screens shared a tie line with the anode metal within the computed convex hull.

These coatings may be employed at nanometer thickness, where ionic conductivity of the coatings does not strongly impact cell impedance. The ionic conductivity for at least some embodiments of the compounds may enable these compounds to be used not just as anode coatings, but also as thick solid electrolytes that enable transport between the anode and cathode.

CONCLUSIONS

It was found that many solid electrolyte and electrode coating materials in the literature react with Li anodes to form unanticipated phases, including phases that are electronically conductive and therefore prevent passivation of the anode/electrolyte interface. The OQMD was screened to identify coatings for Li, Na, and Mg metal anodes that exhibit chemical equilibrium with the anode metals and that are electronic insulators. Ninety-two promising coatings were identified for Li anodes, as well as 118 for Na anodes, and 97 for Mg anodes. These coatings included binary, ternary, and quaternary compounds. For Li anodes, Li-containing ternary coatings were identified, including seven oxides and 21 nitrides, but no fluorides or sulfides. For Na anodes, Na-containing ternaries were identified, including 26 oxides, nine nitrides, and six sulfides, but no fluorides. For Mg anodes, Mg-containing ternaries were identified, including five fluorides, four nitrides, and one sulfide, but no oxides. A variety of chloride, bromide, and carbide coatings were also identified.

Many of the new coatings share similar compositions and can therefore be grouped into classes. Several new classes of coatings were identified for Li anodes, including Li_(x)MN₄ (x=5, 6, 7; M=transition metal), R₂O₃ (R=rare earth), and LiRO₂. For Na anodes, classes of coatings were identified, including R₂O₃, NaRO₂, and NaRS₂. For Mg anodes, classes of coatings were identified, including R₂O₃ and RCl₃. Within the ninety two compounds identified for Li anodes, only Li₃N and Li₇La₃Hf₂O₁₂ have been studied extensively as solid electrolyte materials.

Example 2: Coatings for Lithium Anodes and Solid-State Electrolytes in Lithium Batteries

In this example, the Open Quantum Materials Database was used to search for coating materials that exhibit stable equilibrium with both Li metal and various solid electrolyte materials, that are electronic insulators, and that contain Li sublattices. The requirement for a Li sublattice was relaxed for the binary compounds. The pentenary compounds that passed the screens contained only small concentrations of Li, so these compounds were excluded from the search. The coatings identified include binaries, and Li-containing ternaries and quaternaries. The computational methodology was the same as that described in detail in Example 1.

Coatings that are particularly chemically stable with respect to both lithium metal anodes and various solid electrolyte materials were identified. A general trend can be observed, whereby the oxide and nitride coatings tend to exhibit stable equilibrium with Li₇La₃Zr₂O₁₂, LiLaTi₂O₆, Li₃PO₄, and Li₇PN₄ solid electrolytes, while the fluoride, chloride, bromide, and sulfide coatings are more likely than oxides or nitrides to exhibit stable equilibrium with LiTi₂P₃O₁₂, Li₃PS₄, Li₁₀GeP₂S₁₂, and Li₆PS₅Br solid electrolytes. For example, CaF₂ and YbF₂ are coating materials that are particularly well-suited for coating on lithium metal anodes and also stable on Li₃PS₄ electrolyte materials. And, as another illustration, Li₆WN₄ and Li₂CN₂ are coating materials that are particularly well-suited for coating on lithium metal and also on Li₇La₃Zr₂O₁₂ electrolyte materials. The full set of coatings that are particularly stable on lithium metal anodes and also on various electrolyte materials is presented in Tables 26-32.

Tables 26-32. Coatings that exhibit stable equilibrium with both Li metal and various solid electrolyte materials, including Li₇La₃Zr₂O₁₂, LiLaTi₂O₆, Li₃PO₄, LiTi₂P₃O₁₂, Li₃PS₄, Li₁₀GeP₂S₁₂, Li₆PS₅Br, and Li₇PN₄ electrolytes. All coatings that are listed exhibit stable equilibrium with Li metal. The existence of stable equilibrium between a coating and an electrolyte material is indicated with an ‘X’.

TABLE 26 Fluoride Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂ Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries LiF X X X X X X X X EuF₂ X X X X X X X X SrF₂ X X X X X CaF₂ X X X X YbF₂ X X X X X X X

TABLE 27 Oxide Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂ Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries BeO X X X X X X X X Li₂O X X X X Y₂O₃ X X X Lu₂O₃ X X X Dy₂O₃ X X Tm₂O₃ X X X Ho₂O₃ X X X Er₂O₃ X X Gd₂O₃ X X X Nd₂O₃ X X X X Sm₂O₃ X X X X Pr₂O₃ X X X X La₂O₃ X X X X CaO X X X X YbO X X X X X EuO X X X X Ternaries LiGdO₂ X X X X Li₂HfO₃ X X X LiDyO₂ X X X X LiTbO₂ X X X X LiHoO₂ X X X LiErO₂ X X X X LiScO₂ X X X Quaternaries Li₇La₃Hf₂O₁₂ X X X X Li₁₆Nb₂N₈O X X X Li₁₆Ta₂N₈O X X LiSmEu₂O₄ X X X X

TABLE 28 Chloride Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂ Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries LiCl X X X X X X X X BaCl₂ X X X X X YbCl₂ X X X X X SrCl₂ X X X X KCl X X X X X X EuCl₂ X X X X NaCl X X X X X X CsCl X X X X X X X RbCl X X X X X X X Ternaries Li₄NCl X

TABLE 29 Nitride Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂ Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries AlN X X Be₃N₂ X X LaN X Li₃N X Ternaries Li₂CN₂ X X X X Li₂SiN₂ X X Li₃BN₂ X X Li₇TaN₄ X Li₇NbN₄ X X Li₆WN₄ X X X X Li₇VN₄ X X X LiBeN X X Li₅ReN₄ X X X X Li₆MoN₄ X X X X Li₈TeN₂ X LiMgN X Li₅Br₂N X Li₃ScN₂ X Li₄NCl X Li₄HN X Li₈SeN₂ X Li₂ZrN₂ X X X LiCaN X Li₁₀BrN₃ X SrLi₄N₂ X Quaternaries Li₁₆Nb₂N₈O X X X Li₁₆Ta₂N₈O X X Li₅La₅Si₄N₁₂ X Li₄Ca₃Si₂N₆ X Sr₄LiB₃N₆ X X Li₅Ce₅Si₄N₁₂ X X LiEu₄B₃N₆ X LiCa₄B₃N₆ X Sr₃Li₄Si₂N₆ X SrLi₂CrN₃ X X X X

TABLE 30 Bromide Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂ Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries LiBr X X X X X X X X YbBr₂ X X X X X SrBr₂ X X X X X BaBr₂ X X X X X KBr X X X X X X X X RbBr X X X X X X X X CsBr X X X X X X X X EuBr₂ X X X X NaBr X X X X X X X Ternaries Li₅Br₂N X Li₁₀BrN₃ X

TABLE 31 Sulfide Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂ Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries Li₂S X X X X X X SrS X X X X X X X CaS X X X X X X YbS X X X X X X X BaS X X X X EuS X X X X

TABLE 32 Carbide Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂ Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries Be₂C Ternaries Li₂CN₂ X X X X LiBC X

The word “illustrative” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “illustrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, “a” or “an” means “one or more”.

The foregoing description of illustrative embodiments of the invention has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and as practical applications of the invention to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents. 

What is claimed is:
 1. A coated lithium metal anode comprising: a lithium metal anode; and a coating on at least a portion of the lithium metal anode, wherein the coating comprises a metal oxide selected from rare earth metal oxides, ternary lithium oxides other than Li₃PO₄, quaternary lithium oxides, calcium oxide, or a combination of two or more thereof, and further wherein the metal oxide is stable; exhibits chemical equilibrium with the lithium metal anode; and is electrically insulating.
 2. The coated lithium metal anode of claim 1, wherein the coating comprises Li₂HfO₃.
 3. The coated lithium metal anode of claim 1, wherein the coating comprises Li₇La₃Hf₂O₁₂.
 4. The coated lithium metal anode of claim 1, wherein the coating comprises a rare earth metal oxide having the formula R₂O₃, where R is selected from Dy, Er, Gd, Ho, La, Lu, Nd, Pr, Sm, Tm, and Y.
 5. The coated lithium metal anode of claim 1, wherein the coating comprises a rare earth metal oxide having the formula LiRO₂, where R is selected from Dy, Er, Gd, Ho, Sc, and Tb.
 6. A lithium battery comprising: the coated lithium metal anode of claim 4; a cathode in electrical communication with the coated lithium metal anode; and an electrolyte disposed between the coated lithium metal anode and the cathode.
 7. The lithium battery of claim 6, wherein the coating comprises Li₇La₃Hf₂O₁₂ and the electrolyte is a Li₇La₃Zr₂O₁₂ solid electrolyte.
 8. A coated lithium metal anode comprising: a lithium metal anode; and a coating on at least a portion of the lithium metal anode, wherein the coating comprises a metal halide selected from metal fluorides other than LiF, metal chlorides, and metal bromides, and the metal of the metal halide comprises an alkali metal, an alkaline earth metal, or a rare earth metal, and further wherein metal halide is stable; exhibits chemical equilibrium with the lithium metal anode; and is electrically insulating.
 9. The coated lithium metal anode of claim 8, wherein the coating comprises a metal halide selected from CaF₂, SrF₂, YbF₂, EuF₂, or a combination thereof.
 10. The coated lithium metal anode of claim 8, wherein the coating comprises YbCl₂.
 11. The coated lithium metal anode of claim 8, wherein the coating comprises a metal halide selected from YbBr₂, BaBr₂, SrBr₂, EuBr₂, or a combination thereof.
 12. The coated lithium metal anode of claim 8, wherein the coating comprises a metal halide selected from LiCl, NaCl, KCl, RbCl, CsCl, or a combination thereof.
 13. The coated lithium metal anode of claim 8, wherein the coating comprises a metal halide selected from LiBr, NaBr, KBr, RbBr, CsBr, or a combination thereof.
 14. A lithium battery comprising: the coated lithium metal anode of claim 8; a cathode in electrical communication with the coated lithium metal anode; and an electrolyte disposed between the coated lithium metal anode and the cathode.
 15. The battery of claim 14, wherein the electrolyte is a sulfide solid electrolyte.
 16. A coated lithium metal anode comprising: a lithium metal anode; and a coating on at least a portion of the lithium metal anode, wherein the coating comprises a ternary lithium nitride, wherein the ternary lithium nitride is stable; exhibits chemical equilibrium with the lithium metal anode; and is electrically insulating.
 17. The coated lithium metal anode of claim 16, wherein the ternary lithium nitride has the formula Li_(x)MN₄, wherein x is 5, 6, or 7 and M is an element selected from Ta, Nb, W, V, Re, and Mo.
 18. The coated lithium metal anode of claim 16, wherein the ternary lithium nitride has the formula Li_(x)MN₂, wherein x is 2 or 3 and further wherein, when x is 2, M is selected from Zr, C, and Si, and when x is 3, M is Sc or B.
 19. The coated lithium metal anode of claim 16, wherein the ternary lithium nitride is selected from LiMgN, Li₅Br₂N, Li₁₀BrN₃, Li₄SrN₂, Li₈TeN₂, or a combination thereof.
 20. A lithium battery comprising: the coated lithium metal anode of claim 16; a cathode in electrical communication with the coated lithium metal anode; and an electrolyte disposed between the coated lithium metal anode and the cathode.
 21. The battery of claim 20, wherein the ternary lithium nitride has the formula Li_(x)MN₄, wherein x is 5, 6, or 7 and M is an element selected from Ta, Nb, W, V, Re, and Mo, and the electrolyte is an oxide solid electrolyte or a nitride solid electrolyte.
 22. The battery of claim 20, wherein the ternary lithium nitride comprises Li₃ScN₂, Li₂ZrN₂, or a combination thereof, and the electrolyte is an oxide solid electrolyte or a nitride solid electrolyte. 